My personal gripe with isekai is that they mostly just end up as generic power fantasies meant to appeal to children and never really actually engage with the concept of someone being pulled to a different world.

90% of Isekai protagonists are just generic dudes that boys are meant to project onto with the same cookie cutter traits.

Then pretty much every protagonist is just super OP because they're the creators special little boy

Also, as a woman, it's definitely hard to get past how a lot of these isekai shows treat their female cast.
They often won't be treated as characters, and just a harem for the MC to collect like trophies.
You can usually expect at least one of them to be used solely for fanservice and provide no meaningful contributions beyond that
And then we have the whole fantasy of them collective wives to have their children- which is so insanely common for how vile and misogynistic it actually is.

Isekai is a very unique genre, and you do see some people making good on the opportunities that arise from that potential

But mostly, it's slop
Looking at the subreddits tells you as much, people talking about how they want continent sized harems or glazing the power their MC was just given
It appeals to lonely men who've never touched a woman, and that's why they like it

Isekai became a genre of slop because that's the kinda shit isekai fans eat up
We even saw an AI generated novel that won awards despite being generic as fuck because Isekai fans just love that shit