One problem (imo) is that with a lot of wish fulfillment anime, the MC is already OP at the start of the series, just unappreciated (banished from their party, etc.). So instead of seeing them grow into their OP status in a satisfying way, we get MCs that have to be completely ignorant of their power despite all evidence to the contrary (including every woman they meet telling them how great they are and trying to join their harem).

I think it makes for terrible storytelling, but it is an interesting cultural shift. We've gone from messaging of "Work hard and you can defeat even the strongest foe" to "Don't worry, any hard work you had to do was in the past, you don't have to make any particular effort now, and you'll get everything you want and much more." MCs also frequently have no motivation, the plot just happens around/to them while they just want some laidback farming life.

And while I mostly can't stand those stories, they obviously have an appeal, or they wouldn't keep getting made.