I suspect (i.e., I have not actively researched this): There's this generational burst in feminist waves that corresponds to the time-frame you're pointing out. Teens/20s, the 40s, the 60s/70s, the 90s/Oughts. It's not exact, of course, but I think it's more of a pendulum thing (swings conservative some decades, liberal in others) and very reactionary. That doesn't mean that there wasn't a strong undercurrent of feminist thinking during the lull years, only that it wasn't at the forefront of national discourse.

:) It is totally worth investigating though!