People have both personal and social interests; the latter can overcome the former in a system that people can trust. (Not saying that we have that right now, or ever have)

Ironically, it's usually the opposite, but they've been tricked into thinking it's in their interests.

Copying what someone else said here once...

gestures vaguely to everything

Actually a key element of modern Republican strategy is figuring out exactly how to ensure their base vote against their interests.

In some ways the distinguishing difference for the Democrats is that they haven't proved to be very good at it. "We should fund somebody else's genocide" is against your interest and turns out that selling it as "We're protecting Jews" didn't work very well in their primaries. Tens of millions of idiots voted for Donald Trump, a wealthy rapist who they knew wanted to steal from them and destroy their country, of course they're voting against their own interests.

Generations before Boomers crafted policy that considered the future beyond them (children and grandchildren). Boomers do not follow that tradition.