re: Why aren’t there more open world superhero RPGs?

CoH and Freedom Force have been the best two superhero games.

One big problem with superheroes who have "powers" and don't have a limited set of utilities is the sheer creativity that they inspire/require. It's easy for swords and guns - you have different guns for different effects, or swords...different swipes and moves. Spider-Man works like this because it is mostly traveling and brawling (and Batman again is tool focused).

Imagine trying to make a game around a Vision or Martian Manhunter or Iceman, etc.

A large majority of the environment would have to be built to reflect the power on it. Freezing water, building slides, etc. I think that often gets in the way of conceptualizing something that isn't "tool/weapon/brlawing" focused.