See the “Bernie Bros” who flipped into full Trumpists a few short months later in 2016. I’m sure if you look back at the Spanish Civil War and other divisive historical time periods you’ll find plenty of turncoats that flip from one extreme to another.
This seems like a bit of a myopic, low-dimensional view of the political landscape. Bernie and trump (esp candidate trump) weren't "opposite extremes" when it came to plenty of issues: anti-free trade, anti-corporatist, promises to protect entitlements, complaining about the corruption of the existing political order, even just the populist vs technocrat aesthetic.
For people who prioritize this issue, the notion that Bernie and Trump are "opposite extremes" in every way relative to Hillary is laughable.
(President trump obviously reneged on much of his promises as a candidate and went with many mainstream gop policies, but that's neither here not there when discussing support during the election)
The outcome naturally has a lot to desire.
There really aren't very many of those people.