>>480 (OP)
> Why there aren't much alternative or even just historical
Maybe there is.
It’s just like with everything else, anon. Animu and mangos are not some sort of a magical land automatically banishing the stray clowns to Tumblr and Seattle.
So there’s not much of a niche, and what does exist is going to be hard to find. Especially if you want something better than what passes for “history” in Hollywood and/or incoherent “REEEEE!” of some disturbed wiki-ng about his pet wonk point.
> Nearly every season there is an isekai trash, yuri anime and some other unintresting trash.
Because mainstream shonens for retards, half-assed pr0n and other trash can be churned out by little more than monkeys with typewriters, and there’s always a market for this. Just like with any other medium.
Also, whenever you go looking for good stuff, you have to dodge both the Charybdis of trash piles (where it’s buried forever under vast layers of trashy sediment) and Scylla of the WTF where the hipsters and other basket cases dwell.
The only difference is that with anime most warning signs are visible: the stuff about which the brats babble endlessly and undisguised knockoffs of knockoffs.