It's not uncommon in the more expensive German cities as Munich to do a flat sharing even after you finished your studies. You often did a flat sharing when you studied, so you often are already used to the situation. On the other hand living space is too expensive to be able to afford (even renting) if you don't have a really good paying job.
But perhaps this is a different mentality between US and Germany.
But perhaps this is a different mentality between US and Germany.