Are authors devolving or do studios no longer pick out good stories to animated?

I don't understand, why are some of the popular isekai animes actually lacking in hell lots of areas? There are only a handful actually good isekai animes, others just seem like some guy got bored, wrote about his sleazy life, reincarnated himself into a new world, added a harem of women (who also don't have impressive personalities) and got done with it.