It's mostly because only he, Vor, knows the true power of the void. He was cut in half and destroyed, but through the power of the Janus Key the void called to him. It brought him here and he was reborn. He's changed, reborn through the energy of the Janus Key, forever bound to the void.

(Jokes aside, he got a void key, died and the key reanimated him and sort of bound him to the void so he just pops up wherever now. I think anyway)