My parents are boomer's. They had to take women out "dancing" before there could be any kind of shenanigans. Can you imagine the awkward social phobes of today trying to dance? I think your generation has it easier. You could probably cop a feel on a stayhome date in minecraft.
I think this "incel" shit doesn't exist in a vacuum though. I'm not a sociologist and barely learned the term incel a couple years ago, but I doubt many (if any) incel existed back then. The closest you probably got was extreme cowards/hyper shy/maximum risk averse people.
Think Back to the Future, Marty's dad. He wasn't an incel, he was a nerd who matched the traits I mentioned (shy, cowardly, risk-averse). Those people may have been some type of proto-incel but weren't like what we see today. They weren't violent as attested to the fact that school shootings/female-oriented attacks didn't occur anything like on the scale they do today. That's not even factoring in the ones who don't commit any acts, from what I can tell they're extremely misogynistic.
To pull from film again because I'm not about to actually study 70's/80's proto-incels, contrast the incel with Revenge of the Nerds types. Strip away the comedy elements and that's probably as "bad" as they got.
Nerds were probably what incels were called back then. Today nerds can get laid for a variety of reasons unlike back then, so that's probably why this new(?) term exists, nerd didn't cover the implication any longer.
As society moved toward nerd acceptance you'd think these proto-incels (nerds) would fade out but they didn't, they remained (evolved?). Something else must account for why incels are incels.
Aside from the possibility of complex social dynamics playing a role, the main reason I can think of is they're the ugliest of the ugly. Think "Super nerds," I suppose. Societally irredeemable for reasons I'm too lazy and disinterested in to speculate upon further.