There’s a lot of information, there’s also a lot of misinformation. Many people don’t trust authorities, sometimes for understandable reasons, so they end up in the fringes.
Also, the Nazis, and even the Confederates, weren’t all that long ago in the grand scheme. A couple generations. Many people learn these tendencies from their family.
Also incels are somewhat different from Nazis/fascists. There’s obviously a lot of overlap. There’s always been men who had trouble with women, but I think being a male virgin after a certain age is enormously more vilified these days than it was in, for instance, the 50s, even among more progressive, left leaning groups. Admittedly, that’s anecdotal so I could be wrong.