If an isekai isn't also doing that already that's just the writers being lazy. I haven't watched a lot of isekai, but as a plot device it's just a more escapist flavor of outsider character, something used in lots of speculative fiction as an excuse to explain major events or broad strokes of worldbuilding.

Maybe isekai is just really bad for replacing more interesting world building with exposition or just having really shallow worlds, that seems accurate from what little I've seen and heard. I just don't think clueless outsider characters are a bad storytelling device when used in tandem with environmental storytelling and other less expository world building techniques. Obv showing is a lot better than telling for 99% of situations, but in settings or stories that need some exposition I think explaining stuff to an ignorant character is far from the worst way to do it. Though isekai and similar stuff is usually too escapist for me, and I prefer most stuff just being in its own setting without those kinds of strings attached