I don't hate isekai itself. In fact some of my favorite old stories are technically isekai in the broader sense (The Neverending Story comes to mind).

I hate the creative/metagame rut it's in, where it's so cynical and pandering that modern isekai often acknowledges how copy of a copy it is becoming in its own premise. "Oh wow I died and am in fantasy world just like in my isekais, time to have fanservice moments with obedient fawning dubiously aged waifus that are obsessed over my mediocrity to the point of fighting over it!" :so-true: