One explanation is not about policy at all, but character and honesty.
Trump says stuff, and a lot of Americans have issues with what he says, why he said it.
Way back before he got the nomination, there was a series of clips of him saying "believe me," which I found compelling and disturbing way back when, long before he basically amended his message to be "believe only me" and focused on the media and others when his cult of proud ignorant believers became more "persecuted" (in large part, imo, because not only did the media focus on him, but those who chose to "follow" him.
I'm not saying I'm representative of those who have a particular distaste for Trump's "style", "personality," or way of thinking, but I think there's something relatively unique to him in that his policy positions are not only unconventional and not aligned with conventional party or ideological positions, as much as tailored to what it makes sense for him, in the moment, to say to benefit him, as opposed to any traditional constituency.
It makes Trump, imo, "dangerous" to a lot of people, which, while it works for him, also works against him.
Immigration/open borders/national purity, protectionism, America First, Energy Independence, Windmill phobia, full flushing toilets, punishing uppity black athletes for not kneeling, in the eyes of some, are just comfortable positions for Trump, much like his anti-muslim comments, his pro and AntiLBGT stuff, etc.
I'm just offering my own perspective here, and many other Americans, both Trump fans and non fans disagree.
When I post on Trump, I usually get a couple of critics saying I've got TDS, that everyone is out for himself, and Trump's just more raw, less of a smooth professional politician at talking about of both sides of his mouth, etc, but watch those responses, and see if they don't actually illustrate why he's so "polarizing" in American politics far beyond any particular issue.