Some possibilities:

Visibility effects —

• Bullying of nerds always happened; but it's less shameful for successful adults to talk about having been bullied now; so we hear more about it.
• Scientists have always been weird, but until recently one didn't talk about others' eccentricities. (See, for instance, how treatment of mental illness has gone from locking the crazy person up in an attic or sanitarium, to a matter of public identification.)
• You're young; it looks different when you're older (which doesn't mean either position is more accurate).

Generational effects —

• Going to university once meant that you were both smart enough to pass, and that your family was rich enough to afford it. But the post-WWII boom in public universities (and the GI Bill) meant there were now enough college-educated people for there to be greater intellectual competition for scientific and technical jobs, which favored the more abnormal minds.
• In the 1960s US, being in higher education was a way to avoid the Vietnam draft. Middle America tended to regard draft-dodgers as cowardly, and this emphasized the nerd/jock distinction.
• The rise of college sports as a big-money institution created a nerd/jock dichotomy in colleges which propagated into mass media (especially via popular comedies) and thus into the culture.

Nerds really are uncool (and new) —

• Home computers in the 1980s provided massive intellectual rewards for kids who got into them … at the expense of keeping them home and indoors.
• Differentiation between students headed for science & technical careers has happened earlier and earlier in life, impairing social development.

Other historical effects —

• It's tied to suburbanization. Science was (and is) cool in successful booming cities, but not in conformist suburbs or in socially collapsing cities.
• It's tied to class mixing. Science was (and is) cool among the productive rich, but not among the productive working class, the idle rich, or the lumpenproletariat.
• As science has accumulated more knowledge, there's simply more to learn — and thus a bigger gap between the worldviews of scientifically literate people and everyone else.