WrestlingInc held an interview with Fenix on a podcast episode, and he had mentioned they're allowed to work at any company but WWE. This is due to the fact their contracts are nuts.

Fenix on being allowed to work anywhere but WWE

 “We are in every company now except for WWE… because their contracts are nuts. The time is coming up – I don’t know if it’s WWE. I don’t know. The moment now is the best because I can wrestle whatever wrestler in MLW, whatever wrestler in AEW, in AAW, in Japan, in England, in Mexico…. I’m free and I love it.”