>Why are there so few works that portray Japanese history without some sort of (or a lot of) craziness like Sengoku Basara?
Because people prefer an already interesting premise with its action elements cranked up to 11.
>They don't need to put fantasy shit in it to make it cool, really.
That's kinda self-defeating as why bother animating shit that could be better done (and possibly cheaper) in live action? By the way, there have been already alot of movies that are focused on the Sengoku period era of Japan.