There has always been a tilting towards progressive ideology, whatever that may be at the time, and the nerd phenotype. Physically weak people, the unattractive but smart, these types of people are in a majority sense going to be drawn towards the hot new thing.
I think it's less about the "hot new thing" and more about the opinions towards society and other people that certain formative experiences tend to inculcate in people. Using myself and many fandom friends I've known as examples, several childhood characteristics tended to be common among the Western fan-geek population, especially in the '70s and '80s:
- Frequent humiliation and/or rejection by peers, usually as the victims of bullying or teasing based on unusual interests, or genuine gaps in intellect and/or maturity.
- Generally better experiences with teachers and adults, especially if the adults encouraged those interests rather than mocking them.
- Personal familiarity with family collapse, either their own or a close friend's or relative's.
Assuming formative experiences like these always seemed a very plausible explanation for many of the traits I've seen demonstrated by fervent progressivists (and which I possessed a few of to some degree myself, back in my more centrist days):
- contempt for popular taste and opinion;
- admiration for benevolent authority figures who could use their power to redress injustices and share things out fairly;
- the belief that society would do better if run by a small gifted elite than by leaving the hoi-polloi to themselves;
- disdain for "traditional families" and the impatience with any arguments that such families were best for both parents and children;
- the desire to characterize rejection, criticism and condemnation (even purely verbally or philosophically) as socially destructive assault when done by the majority to the minority or the powerful to the weak, but to embrace it as moral and heroic when done in reverse. (This is, of course, one of the first things to change now that progressivist philosophy has such a stranglehold on certain key channels of social power.)