I get that stands have more creative potential but I do wish at least occasionally hamon would still appear in the series, it's such an interesting power.

They took over because Araki moved on from vampires. Simple as that. And due to the way Hamon was written in those first 2 parts, it doesn't really have any use beyond "they can do crazy things" if there is no more vampires.

Stands on the hand can be whatever Araki feels to create or draw. They don't have any limitations or mayor set of rules