The reason is kind of important, no? You can shrug and say idiots and racists, but that's far from the whole story, not really even the primary reason. A big piece of it is people feeling disengaged from politics, which is understandable, since U.S. policy hasn't reflected the will of the people for almost 50 years now.

More or less telegraphing that "I will not listen to what you want" and "I support evil but have the decency to feel bad about it" (like on Gaza, for example) is not a great way to motivate people in this environment.