The anime isekai genre is facing a problem. Many anime are repeating the same tropes and story beats. Minimal effort is being put into making one isekai different from the other and pushing the genre forward. The most anyone can think of is to make the Hero reincarnate as one of many things (a slime, a spider, a sword, a vending machine, etc.), make them overpowered, and have them sweep through the early series. These anime rarely earn another season because of how quickly audiences lose interest. Once the unique premise has been shown and the rest of the series turns out like every other isekai, there's no further reason to keep watching.
Source：https://www.cbr.com/rise-of-post-demon-lord-anime/
