the aspect people get attached to the most from it is the wish fulfillment of being immediately godlike in a new world. We're already seeing other genres popping up in popularity, right now there's a boom of romcoms where MC gets effectively married to some rich/popular girl after getting in debt for no reason other then they had a secret crush on them.
Isekai is an easy to write excuse for why a MC gets transported to a new world and is a blank slate but its gotten to the point where its so overused you can pretty easily tell the difference in quality from the start