To more directly and accurately answer the questions asked, it's because most people in the U.S. are willfully deluding themselves that what's clearly happening, isn't, because to acknowledge our awful reality would require direct personal action and sacrifice, which most citizens reject.
We're a nation of people who choose to live in a fantasy of "it's not that bad" or "the system will stop him", rather than to do all that must be done.
We're mostly either lazy cowards, or gleeful participants, as we're confronted with the relentless horrors of authoritarian rule, in general, and fascism in particular.
It's how we've long been systematically conditioned and worn down over the brutal history of this fundamentally evil nation literally built on genocide, slavery, and the utter subjugation of those dependent upon wages for survival.
We're the near-perfect capitalist state, and this is how we end.