Although the series prides itself on having morally grey characters, Tywin was a source of antagonism for many of them. After Tywin died, there was a "villain vacuum" and no character filled that gap. This was cited as a major problem in the last two books. Yeah you had people like Euron and Book Ramsay, but they are unknown to many of the characters and don't really accomplish a whole lot. Much of the conflict in the last two books are caused by internal issues or unknown and unexpected sources (Harpies, Faith Militant, Night's Watch traitors etc.)
The show tries to rectify this by trying to make Ramsay someone for the audience to focus their ire on. But while Tywin and Ramsay are people you love to hate, Ramsay is someone you just want out of the way so we can get to other things.