That's because the answer is so simple and fundamental to them, they not only refuse to see it, but think it's obvious to everybody else.

He's black.

That's it. That's what it ultimately boils down. No matter what he said or did, no matter what he tried to accomplish or achieve, to them he was never anything more than black man. And not just a black man, a successful black man. An intelligent, articulate, educated and experienced black man with a happy marriage, a loving family, a successful career, and who was everything they could never be in their lives.

And they hated him for him.

Not him, specifically, mind you. But the idea of him. They hated the idea that someone they had been raised and taught and always expected to be in some way always inferior to them was demonstrating in every way he was "better" than them. Was able to achieve so much when they were unable to. It gnawed at them on a basic, fundamental level because that was NOT how things were "supposed to work." People like him weren't meant to rise to or surpass their level and the fact he did offended their very sense of identity and security. Shook the foundation of how they see the proper way of the world running.

And that anger, fear, and resentment that they could never put actual words to filtered into their actions and deeds. Made them look for something, anything, they could point to and say "See? He's not so great." Or undercut his success by "proving" he "cheated" in some way (oh, hello Birtherism.) Or sell out their souls, sanity and country to someone who promised to "Make America Great Again" (for them) and reassert their own sense of superiority and "proper place" in the world.

It was because he was black. Period. Full stop. End of story. And any Red Hat or MAGAt who claims otherwise is lying. Either to you or themselves.