...because while you are significantly more likely to encounter casual expressions of say sexism or sexuality / gender based discrimination, casual critique that nowadays is mostly far to the left of the average person's worldview was also significantly more common.
Simply the left leanings of intellectuals like the kind of nerds that were making anime in the 70s after spending university years in a Maoist organization (and eventually drifting back to liberalism)?
Genuine sympathy among the workers involved in making the show, such as when they obstructed the making of that right wing WW3 anime movie? (Future War Year 198X, 1982)
The kind of moralizing about the evil empire from the 50s and 60s growing unpopular (+ the Ls the west took around then) for a bit and Corn Man's "policy of peaceful coexistence" becoming mainstream even among average liberals?
Liberal nationalistic concerns that the confrontation between cold war blocs was merely something Japan was stuck in and was harmful to it? Europe had a lot of that, even in the 2000s!
Probably all four!
The source is Combattler V, Episode 2 (1976)
There was a comment by someone here a long time ago that linked to an article, whose thesis is that the first otaku were radical students, who in the face of defeat of direct action, retreated to their local clubs and made their own works