It's not that change is bad, but they just went about executing it in really haphazard ways.
I don't want to drag a dead horse out to beat and derail the thread, but an example would be how they mangled the Inhumans to make them the new mutants, which didn't suit either (and their fans) well. Needless, sullied the fans, and ended-up failing and being walked-back after they kept doubling-down.
Another would be benching so many of their hallmark characters - currently being heavily featured in movies, mind you - for teenage replacements, very quickly. Marvel's takeaway was "people don't want diversity", which was absolutely incorrect; the problem was that they introduced all of these teens (in their new roles, like X-23 and A. Cho) all at once while simultaneously killing - either medically or via character assassination - the long-time favorites. ("People" are also just getting bored with a mostly creatively-bankrupt Marvel and buying less of their stuff.)
Nothing means anything anymore, because editors aren't interested in coordinating, making everything inconsistent, and characters are commonly getting killed and sometimes getting replaced. Meanwhile, the status quo of the world changes too frequently - before we can even understand what the status quo is, and what the stories are, we get a "new earth-shattering epic event that changes everything as we know it".
I'm all for the world developing, characters growing, rosters changing, etc., but I'd just preferred they went about it in the interest of telling good, well-written stories that will stand the test of time and not hurdling from one editorial mandate/bad story idea for quick cash infusions to another.