Vets push it because most American's are not responsible owners and can't keep their pets from "accidentally" reproducing.
it takes a lot of supervision and there are other issues that can arise like aggression esp towards other males
also as mentioned prostate issues down the road
and other reproductive cancers
there is always a trade off
also looks are determined more by genetics than early neuter except there seems to be a propensity towards extra bone growth making the dog slightly taller if neutered earlier than later