Q:

Why didn't battleship Bismarck have more support?

The primary objective of battleship Bismarck was to sink transporters coming from the U.S. and sailing to Europe transporting goods (oil, food). It encountered HMS Hood and sank it.
German cruiser Prinz Eugen was sailing along with the Bismarck all the time apart from the time the Royal Navy engaged heavy forces to sink it.
Why didn't the Bismarck have decent battleships, carriers and other fleet types sailing with it all the time? It was certain to German admirals that after the sinking of HMS Hood the Brits would employ forces in order to destroy the Bismarck.
Why didn't Otto Ernst Lindemann (naval captain, only commander of the Bismarck) ask for reinforcements after the HMS Hood event?

A:

The Germans wanted to send more, but there were none available.  Most were unsuitable to escort Bismarck.  Those which were suitable were damaged.
A good warship for commerce raiding is fast, both to catch enemy ships and run from warships, fuel efficient to keep at sea for as long as possible, and carries heavy armament to rapidly sink enemy ships from long range.  Bismarck could make 30 knots and cruise for 10,000 miles, there were few heavy ships in the Germany Navy which could keep up.
Her sister, Tirpitz, was still working up. The battleships Scharnhorst and Gneisenau were both under repair in Brest on the wrong side of the North Sea.  The old pre-Dreadnaught Deutschland battleships were far too slow.
Germany had build a small fleet of brand new Admiral Hipper heavy cruisers. Blücher had been sunk, Admiral Hipper was being overhauled in Kiel, Seydlitz was never completed, and Lützow had been sold to the Soviets. Prinz Eugen which was damaged but hastily repaired and ready.
This left the older and slightly slower Deutschland class "pocket battleships" designed as commerce raiders. Of the pocket battleships, Admiral Graf Spee had been famously scuttled in her own commerce raid. Lützow nee Deutschland had recently finished repairs from a British torpedo attack and was waiting to go on its own raid with Admiral Sheer. Admiral Scheer had just returned from a five month long shipping raid in the Atlantic and was undergoing repairs in Kiel.
The rest of the Germany Navy was light cruisers, destroyers and smaller ships.  While they had the speed, they did not have the endurance.  They also didn't have the firepower.  The heavy 203mm and 380mm guns of the Prinz Eugen and Bismarck will be in range long before the 150mm guns of a German light cruiser.  Since you're not planning on fighting a fleet of warships there's no need for a screen of light ships.  They're just a liability.
As for carriers, Germany never had one.
Bismarck was used as a commerce raider because she could destroy most British ships before they could even get in range and run from the rest.  Prinz Eugen was the only available consort.  But they were caught by equally fast and powerful units of the British Navy sent to find them, the Hood and the Prince of Wales, and forced to fight.
Sending more warships risks the commander thinking they should be fighting enemy warships.  This was not their mission, though the German commanders often did not agree.  The diminutive German Navy had no hope of defeating the Royal Navy in a fair fight on the high seas, but it didn't stop officers from thinking they could, especially with a ship as new and powerful as the Bismarck.  Captain Lindeman, commanding Bismarck, was eager for a fight to use his powerful new ship.  But Admiral Lütjens strictly held them to their mission.

Then there is the problem of supply, in particular food and fuel.  A successful commerce raider will be out as sea for as long as possible.  Even if they fail to sink a single ship, their existence can tie up enemy naval assets hugely out of proportion.
A commerce raider can resupply from friendly overseas ports, and from friendly supply units, but mainly from scavenging from the commerce they raid.  The more fuel hungry warships you have in your fleet, and their very large and hungry crews to feed, the more thinly you need to spread your supplies.

The Bismarck's mission was to raid commerce, not engage enemy warships. A good commerce raider will hide or run, only as a last resort should it fight.  Why?  It jeopardizes its mission of raiding commerce.  Fighting a warship risks damage, damage that could force it to return to port early (thus aborting its primary mission), or make it vulnerable.  The Bismarck's victory against the Hood caused both these consequences.  The Admiral Graf Spee had a similar fate after its victory in the Battle of the River Plate.
Even with no damage, engaging a warship means firing a lot of precious main battery armament.  Fuel can be taken from enemy ships, but ammunition cannot be replaced without returning to port or a risky at-sea resupply mission.  Resupply at sea leaves you stopped and vulnerable with more ships for the enemy to track.  Returning to port both cuts short its primary mission, and it leaves it open to bombing and blockade by the much more powerful British Navy, as happened to its sister Tirpitz.
If you sink a Royal Navy warship you risk the wrath of the Royal Navy, far more powerful and numerous than the German Navy.  It makes it difficult to raid commerce when you're dodging an ocean full of British warships.  It happened in WWI after a German victory by von Spee's powerful commerce raiding squadron at the Battle of Coronel, they were destroyed a month later by an even more powerful British task force sent to hunt them down at the Battle of the Falkland Islands.
Sinking the Hood, pride of the Royal Navy, and in such a spectacular fashion, signaled the death of the Bismarck, failure of her mission, and the loss of an irreplaceable German battleship.
See Also

Operation Rheinübung - First and Last Voyage of the Bismarck by Drachinifel

A:

As identified in the first paragraph of the question, the purpose of Operation Rheinübung was a continuation of the commerce raids on allied shipping in the Atlantic. The Scharnhorst and Gneisenau had previously performed a similar exercise with great success.
Commerce raiding was a common tactic used against a superior (or simply numerically larger) naval force. It allowed the smaller force to do disproportionate damage against the enemy shipping while avoiding the risk of putting all of their warships at risk at once. By keeping their own ships dispersed, the Germans would force the British to spread their own forces to find and attack them. In that situation, there was the possibility that the German battleship would be able to out-fight the force it encountered (or simply out-run, as was the case when the Scharnhorst and Gneisenau encountered a couple of British battleships). 
Had the Germans committed a larger flotilla (or even fleet) to the operation, it would have allowed the British to concentrate their forces too. In a fleet action the Germans would have, almost certainly, been outnumbered and outgunned. In which, case they would have been at risk of losing a considerable part of their surface fleet in a single action. 

A:

As far as "battleships" go, the Germans only had the Bismarck. The Tirpitz had just completed construction and wasn't quite "ready" for major duty, and the battle-cruisers Scharnhorst and Gneisenau were undergoing repairs.
A more interesting question is why didn't Germany send out cruisers and destroyers with the Bismarck to protect it from "cheap shots." Apparently, no one felt that they were needed. The Bismarck originally had a cruiser escort, the Prinz Eugen, that did a great job of shielding the Bismarck against the opening fire of the Hood. But Bismarck's Admiral Luetgens apparently didn't feel the need for such an escort, and detached the Prinz Eugen for "independent" duty. The idea was that the Prinz Eugen could do more damage by itself than by accompanying a Bismarck that was damaged, and needed to head to port for repairs. 
With benefit of hindsight, the Prinz Eugen's anti-aircraft fire might have helped save the Bismarck from air attack by the bombers of Britain's Ark Royal. But that's with hindsight, because no one thought in those terms at the time.

