Low-income voters are disproportionately minorities, who often likely couldn't bring themselves to vote for someone with an overtly racist/nativist platform. For me, the surprising number is how many (especially hispanic voters) actually did vote for Trump. It was an eye-opener when my (black) mother said that she was going to vote for Trump early on in the election cycle, although I'm fairly sure she didn't in the end (I think she chose to leave her presidential pick blank.)
Clinton had the distinct "cultural" advantage IMO, although evangelical voters united fairly monolithically behind Trump; the marketers of culture lined up pretty solidly behind Clinton. It's also important to remember that the culture of white dudism only represents about 1/3 of the country, although it represents a bit higher percentage of voters, and there were a lot of young defectors this cycle.