They can, and my statement is a bit of a caricature (it's not like I expect the person pouring concrete to be mixing baby formula a year later) but it seems like "but amenities!" is mostly a way to make sure any new arrivals have to pay for things for existing local residents. Development charges are similar.

Land and real estate is not unlimited especially in urban areas. Building companies optimize for profit so they don't have a good incentive to build out public necessities. It will be always a bit of squaring a circle if you want half sensible area development.