I'm pretty sure Berlin has public transportation. I have it here in Trondheim, Norway - but only one town that I've lived in the states had busses. They didn't run all night, on Sunday, nor did they visit all areas of the somewhat small town. (I'm from the US, lived more places there than I have in Norway)
Other places had taxis (that you couldn't order ahead of time to get to work on time) and some had none until they uber/lyft. (Don't know the current situation).
I'm going to guess the other thing Berlin has is safe areas to walk. I can go to a party and walk home, safely on walking paths complete with shortcuts, without even being harassed by the police and risk getting arrested and in jail for the night (for public intoxication). None of these were luxuries I had in the states.
And I'll say that yes, I've been in some small apartments - but only some folks with small apartments can host. You probably have no clue how many would host if they only had enough space, but a small apartment with 2 adults that have hobbies limits things.