Honestly I was just thinking about this - there have been many manga series (which get turned into anime eventually), that started out with an interesting premise that can be taken into many directions, only to turn into a cookie-cutter shonen battle manga.
I think I know the reason for this - shonen is a relentless popularity contest, where magazines only feature the most popular works and will quickly drop your series once it starts losing readers.
The way to consistently stay on top is to appeal to the biggest demographic - that is shonen battle/isekai fans by making your stuff to be exactly like the other stuff.
But doing so makes you lose the readers who were interested in the thing that made your manga unique in the first place. And after a time, these people will stop reading the publication altogether, skewing fan demographics even more towards genre fiction, making it even more impossible to create something unique.
I think I know the reason for this - shonen is a relentless popularity contest, where magazines only feature the most popular works and will quickly drop your series once it starts losing readers.
The way to consistently stay on top is to appeal to the biggest demographic - that is shonen battle/isekai fans by making your stuff to be exactly like the other stuff.
But doing so makes you lose the readers who were interested in the thing that made your manga unique in the first place. And after a time, these people will stop reading the publication altogether, skewing fan demographics even more towards genre fiction, making it even more impossible to create something unique.
I have seen this happen multiple times.