Requiring two egresses usually means that the building will not have an apartment that spans the width of the building, instead there will be a central hallway to connect every apartment to two stairwells.

That central hallway seems small, but it eats a fairly substantial percentage of the footprint space of the building. (elevators and trashrooms are also examples of things that eat a lot of footprint; limiting them for smaller buildings is beneficial for floorplan efficiency)

And since people do not like bedrooms without windows, having apartments that don't span the width of a building limits possible floorplans, and drives the apartment design towards studios and 1 bedrooms.

The buildings tend to become very wide in order to accommodate enough apartments to make them worthwhile to build, so they tend to use up a high percentage of the lot they are sited on, which reduces greenspace and other resident amennities.