The Bismark and Prince Eugen had a destroyer escort for the first step of their journey but were left to break into the Atlantic alone. Why didn't the Kriegsmarine sent a fleet to the Atlantic alongside the Bismark? I understand that the Germans were not looking for a large-scale naval engagement but surely as soon as the Bismark had commenced her intended mission and begun convoy raiding, the British would have sent ships after her anyway? So what was the intention in sending just two ships to perform the job of a fleet?
This previous thread which I contributed to might help answer this -- it's really /u/dbht14's comment at the top that you need.
This is also a great answer from /u/thefourthmaninaboat: https://www.reddit.com/r/AskHistorians/comments/3f201d/why_was_the_bismark_not_given_more_protection/
Convoy raiding was not the job of a fleet. German commerce raiding doctrine called for single capital ships, or armed merchant ships, to roam around the ocean, using discreetly positioned fueling stations to resupply. All of Germany's surface raiders operated this way, from the Graf Spee, to the Kormoran. Bismarck was no different.
There was a practical element to this as well. Raiders needed large fuel stores, to cover the long distances involved, and to prevent frequent refuelling would make the raider vulnerable.
The Bismarck and Deutschland class ships had ranges of about 8,000 nautical miles, while existing German destroyers only had 2,000. For reference, if a German destroyer attempting to take the same route as the Bismarck, it would had to have turned back before even reaching where HMS Hood was sunk.
Capital ship surface raiders ended up being pretty cost-ineffective, so if you were thinking that Bismarck's expedition was a bad idea... you might just be right.