Bill Gates is actually very concerned with reducing population growth.

I think you have an OK point and the more intelligent rich people like Elon Musk are the ones furthering your agenda. Bill and Zuck were always too conventional to think big like this. Their conventionality was part of their success--they are both too uncreative to come up with something new but instead they know how to steal the ideas of others and make a more competitive business out of them.