Originally Posted by
80sForever
X-Men (Marvel mutants in general) always felt so different to me than the rest of the Marvel Universe that at some point (maybe under Morrison or as a result of House of M) they should have existed on their own earth.
Even with 1970s Claremont and with some mutants crossing over into other comics like Ice Man, Angel, Scarlett Witch, Quicksilver, Beast, and Wolverine, the mutants always felt like they were from a different editor/publisher.
From the 1960s until the 1990s, I guess the rest of the heroes were on vacation when the Sentinels attacked.
Once Uncanny started spinning off their own titles (New Mutants, X-Factor, X-Men, etc.) and had their own crossovers, and eventually an entire country with millions of mutants, the writing was on the wall that it would have been simpler and more realistic for them to live in their own world.
Stan and Jack's X-Men felt part of the original MU but after they left- not so much.