Fair question. Aliens could take over if they wanted to at any time due to technological disparity. So Eisenhower allegedly made a deal with the greys. Wonder what was so bad about what the Nordic aliens offered? I'm willing to bet something something worldwide full disclosure something something.

Anyways what I was inferring is that why would a giant race and/or other races in the center of the sphere not take over at some point?

They are not above reproach. No one is. Gilgamesh was a dick.

Maybe the outside of the sphere, while nice, is a fucking deathtrap.