The first thing that comes to my mind is that you either have to commit to have the entire habitable portion of a station be rotating, or you have to have some

The first thing that comes to my mind is that you either have to commit to have the entire habitable portion of a station be rotating, or you have to have some kind of rotating joint that connects the rotating and non-rotating parts of the station. That joint has to not leak air and be very reliable (if it seized up, the station could tear itself apart from the sudden torque). Having the whole habitable part of the station rotate may be fine most of the time, but it makes docking with ships more complicated. If the ship can't be spun, then you can either use some kind of rotating docking collar (which doesn't have to be perfectly airtight if it's only used once in awhile, but it still has to be pretty good) or you have put on a suit and do a spacewalk just to move things back and forth between the station and the ship which sounds kind of inconvenient. (I guess there's actually another solution which is to stop the station spin whenever docking with a ship. That costs energy and/or reaction mass, though, and you'd have to deal with whatever disruption switching to zero-gravity brings.) I can see why they might not have wanted to deal with this for ISS, but maybe for a bigger/more ambitious space habitat we'll want to do it.