Rules that all units need 2 different staircases really dictate the sort of layout that is physically possible, nearly always resulting in a long central hallway with stairs at either end that feels very impersonal. The resulting units are also not great places to live, with windows on a single wall. Every bedroom needs an egress window, so building 3+ bedroom units almost never pencils out. It's all 1-2 bedroom 'starter' apartments, rather than the types of beautiful 'for life' apartments you'd see in pre-war new york buildings.
Since the staircases are required no matter what, developers are incentivized to stretch the horizontal distance between them as far as possible to amortize the space penalty of the stairs, making the building feel even more impersonal once inside.
If single stairs plus a sprinkler or other fire suppression was allowed multifamily buildings could be set on much smaller lots, with more corner units that have windows on 2 sides or even small, skinny apartments with half or the full floor dedicated to 3-4 bedroom units. The interiors would have far more light and the buildings would be much more human-scale, all contributing to things feeling a lot more personal. There could also be a lot more green space and gathering space scattered in smaller parcels, breaking up the hulking 5+1s we have all become used to.