There is a level of passion and commitment to crossfit that other disciplines don't always have, and due to the way it's practiced it's really beneficial to have your own space for it so crosfit tends to happen at crossfit only gyms, at scheduled times amongst regular practitioners.

To keep riffing on the religious theme, there was a fair bit of controversy around crossfit when it first arrived on the scene, to the point where even other fairly similar gym disciplines were pushing it out of their gyms. That kind of criticism tends to drive you back into your group (the same way door-knocking drives evangelists back to the warm embrace of the parish), and I almost never see crossfit happening in regular gyms, just crossfit gyms. As above that's partly practicality, but I think it's also fair to say it wasn't received well at first and that likely drove people to those specialized gyms instead of practicing it at their local.

I do powerlifting/strength training and powerlifters had the same issue in mainstream gyms, and there are powerlifting specific gyms around. But that's gotten better over time with mainstream gyms having powerlifing/olympic lifting gear more often than not now.