@Ibri
You're not wrong. I think the main reason isekai is done so much (besides following the money) is because they're mostly written by newbie authors who aren't confident in their ability to drop exposition normally. An adult native to a foreign fantasy world is going to know things the readers don't no matter what, and children aren't normally mentally mature enough to be a perspective character while receiving exposition (reincarnation fixes this, but someone from the same world would know already and someone not would make it an Isekai).
I do agree that we need more application of "outside perspective", though. Strangely, the first example of this that comes to my mind is Titus from Final Fantasy X. He's someone in a totally foreign world-technically an isekai protagonist-and needs to have everything explained to him.
But the writers don't stop there with it; he often innocently asks "why" when he gets explanations and starts getting people to wonder and question the reality they've lived their entire lives in.