Not trying to be a mindless skeptic but your “why is it so hard” question seems bizarre to me. It seems quite understandable that it’s hard for people to believe there’s a particle responsible for a significant percentage of all matter in the universe that we have no direct evidence of and the only reason it’s believed to exist at all is because a lot of otherwise well-understood equations and observations require it to exist.

"the only reason it’s believed to exist at all is because a lot of otherwise well-understood equations and observations require it to exist."

I mean...those are pretty good reasons. If a particular theory successfully predicts more out of "a lot" of observations than any other competing theory does, and is a smaller departure from "a lot" of existing theory than any other competing theory is, would you choose to spend your career researching those competing theories?

If people understood that the last 200 years of science has shown that we are still utterly ignorant about the underpinnings of the universe, they might accept it better.

But we are not very well educated so yeah, they will doubt it for no good reason other than "it doesn't feel right"