It's normal there are many of them because they're an efficient way to start power fantasies. They're in the same vein as time travel, rebirth, and resurrection. The point is to have an easy clean slate to start a new life of being a badass in a fantasy setting. What's sellable are power fantasies. One of the tried and tested ways to start them is isekai. Experimenting and reinventing the wheel can lead to very interesting stories BUT will readers even go for that? Only a few. (Speaking from my own experience writing different kinds of stories.)
In topics like these, don't blame the writers, blame the readers. It's natural writers want readers to come, and this is what readers want so writers provided it. Trying something new is very risky and will usually lead to failure.