>>91451480Since it wasn't actually explained:
Once upon a time, there was an event called House of M. It started when Scarlet Witch suffered a mental breakdown and decided to rewrite history. No, this is not something she can actually do; her power is probability control, not omnipotent reality warping. Anyway, one bright flash of light later, and the entire world is changed to a different one. Mutants, instead of being a persecuted minority, are a ruling class, while normal humans are oppressed and marginalized. Also, lots of characters seem to have better lives in the new world, but no one remembers the original world.
To make a long story short, they find out what happened and try to reverse it. Wanda has another nervous breakdown and decides "no more mutants", which means that things are now like they were in the regular Marvel universe except nearly all the mutants on Earth lose their powers and become normal humans. This results in things like people with the power of flight dropping out of the sky, hate crimes against some now-powerless former mutants, and mutants overall becoming an endangered species. Of course, the vast majority of affected characters were secondary or background characters; all the important ones like the main X-Men team either got to keep their powers or regained them quickly.
Apparently, the reason for all this is because someone felt that there were so many mutant hero groups that mutants were starting to seem like less of a minority. They even had their own cities and cultures! So they decided to give a character new powers and have her use them to commit genocide.
