Except the Avengers don't. They are constantly coming to the X-men's aid. Whether it's by writer's choice to show the threat level or just how it is, if you Google "Marvel Events" you'll see a precedent of the X-men standing aside for whatever reason and the Avengers always getting involved (or butting in depending how you look at it). So when there's a dome Bastion put around the X-men's San Fran base, Thor, Iron Man and the FF are trying to beat it down to help the X-men. Mutant Massacre? Thor is in the sewers fighting Marauders. Onslaught, The Avengers had to seemingly sacrifice their lives to fix that mess. The X-men LOVE to and probably need stay in their lane (for safety) and I don't blame them, but most other teams are constantly interacting. Inviting some of the FF and Avengers to the Gala is a no brainer. You have to gain their trust or they'll come for you because you are harboring mass-murderers under your new laws. But screw the Inhumans who inflicted themselves upon the world via Inhuman pollen-sperm cloud.