Treating this as a serious question: because the big reactor in the sky has a built-in gravity well and a very big sphere of vacuum that works as a free contain

Treating this as a serious question: because the big reactor in the sky has a built-in gravity well and a very big sphere of vacuum that works as a free containment system while still letting just enough energy out to be useful. Also we don’t need to refill it or handle the spent fuel.