Several of the shoujo "Oh no I'm the villainess!" isekais are actually very highly rated.

Don't hate the genre, hate the poorly written trash that gets picked up for an anime because their publisher wants to promote the trash novels. This same cycle happened to Magic-Meets-Science series, and magical harem series, and space series, and even high school romance series. Isekai persists because they're easy to write when they're shitty.

Relatable protagonist for the readers to connect with or insert themselves. Being transported to a new world, exposition is required so the author doesn't have to show anything when they can simply explain it all, secret powers or rule breaking powers remove the need to write intelligent conflict. And so on.

The good series either don't do that.

UchiMusume is also definitely NOT an isekai. By saying that, you're conflating all light fantasy with isekai.

@shinta: SAO isn't isekai, but Log Horizon 100% is one, unless it changes genres more than halfway through its current run.