Why don't new buildings have fire escapes?

Same reason dial telephones haven't been manufactured since the 1970s and new vehicles for the consumer market do not have carburetors (with the exception of a few isolated 3rd world markets). Better technologies exist.

Probably because new buildings are built to upgraded safety standards in addition to having sprinkler systems. Good question - the only fire escapes I have seen lately are in the movies.

designer, owner and contractor of the building is responsible for this

An abundance of superheroes.

Self-enclosed fire safety stairwells, with self-closing fire-resistant doors the only access between floors.

It depends on the local fire & building codes.

Too many people anyway, time we got rid of a lot of them.