"Sometimes it is a fantasy held by genuinely popular people annoyed that post-high-school contemporary life doesn’t reward popularity in the ways that they’ve come to expect that it should." What exactly do you mean by a "genuinely popular person"? Doesn't popularity vary over time and circumstance? Aren't people still rewarded for being well-liked after high school?

This is complicated, but the short answer is; high school is (essentially) a universe of people who are thrown together in a confined space and told that they’re not allowed to leave.  In such universes, social skills are incredibly all-consumingly important.  There’s going to be some kind of social hierarchy, because humans, and there’s nothing to define it except the vicissitudes of popularity; being on top means that you’re protected from rivals and threats, and that you get to boss around all those people who are stuck in the hellpit with you.  Prison works pretty much the same way.

(And, yes, what exactly makes people “popular” will vary from hellpit to hellpit.  The top dog queen bee cheerleader is unlikely to have the same skill profile as the top dog gang leader in supermax.  That said, certain traits almost always help: confidence, ability to read people and respond quickly to their emotions, ability to read trends and get on top of them, etc.)

Once you’re not in a hellpit anymore, being social top dog loses a lot of its power.  People don’t have to fear you or suck up to you, they can just ignore you.  If you’re not offering them resources, they’ll go look for someone else who will.  If you try to bully them, they’ll…walk away, and (under most circumstances) you can’t follow after them without being a pathetic low-status creep.  Instead, to get resources or social prizes, you have to have something positive to offer.  Being generically good at making and maintaining alliances still helps here, a lot, but so do a lot of other things.  (“Having marketable skills” is a big one.  “Sharing hobbies or interests” is another, mostly relevant in very different contexts.)