Even if they did add basic collision physics to hair, it has to go 'somewhere'. When you add a brick wall to the clothing, and then of course the body, first thing its going to want to do is find the path of least resistance, straight out the side or up (or mangle itself into a pixel ball). So to make that look natural they'd probably have to add more joints, increasing cost in performance. Then of course if you add this to each character out there, that probably would be valid use of 'system limitations', although more on the users end.

If they can't even get themselves to give slightly altered looks to clothes for tails, I doubt this even crosses their mind for the 'to do' list.