It's not a big deal if you don't mind camped space. If you look at a tower like Park Avenue West and its floor plate is roughly the size of Park Place except PA puts 12 units on a single floor plate vs Park Place which is 10, that is 2 additional units worth of space taken from the other 10 in essence.
So everything pound for pound is closer. Not to mention if they have 3 elevators, it is just that more delayed for people on higher floors. Park Place was bad enough with 3 elevators that at times you would wait in the lobby for 15 minutes before you could take one to the higher floors.
So in Park Avenue get used, around rush hour, to wait in the lobby 20-25 minutes for an elevator. For reference, it takes me about 25 minutes to drive from South Delta to Surrey Central so in the same time I can drive home, you stand in the lobby waiting for an elevator.
FUN TIMES.

So cramped space, long elevator delays = high density tower living.
I agree that it should be 6 units per floor, 8 in a pinch in general but that just won't happen anywhere now I'd say. The 10-12+ units per floor towers sell so why would a developer not build them they get an exponential increase in profit from extra units on a single floor.