The X-Men depended too much on the "we're persecuted" theme since they did Days of Future past in the 80's. Then Legacy Virus, E for Extinction, House of M, etc. They've become the opposite of what people grew to like. People even attacked the inhumans for adopting this theme because "this only happens to mutants and it's their trademark." Now that they abandoned that trademark and adopted the inhumans' theme, it's okay.
And comic book readers don't like change that much. Some do and get on board. If this era was written during the All New All Different period, I wonder if fans would've been happy since everything Marvel did at that time was bad according to a lot of people, including the inclusion of obscure characters and the inclusion of diversity. I didn't mind this period, but when they returned to legacy characters, they did better with sales I think. People just panicked because they actually thought legacy characters weren't coming back. It was click-bait websites that fueled this too.
Here's a quote from The Guardian about the ANAD era:
But speaking at the Marvel retailer summit about the studio’s falling comic sales since October, David Gabriel told ICv2 that retailers had told him that fans were sticking to old favourites. “What we heard was that people didn’t want any more diversity,” he said. “They didn’t want female characters out there. That’s what we heard, whether we believe that or not.”
He added: “I don’t know that that’s really true, but that’s what we saw in sales … Any character that was diverse, any character that was new, our female characters, anything that was not a core Marvel character, people were turning their nose up.”
This is probably why newer mutants don't get bigger fanbases and fade away with time. Not even the writers see them as core characters. Especially if they aren't tied to legacy characters like X-23. And a lot of fans have their favorites and rarely stray from them.