During the postwar years a lot of (white, middle-class) Americans enjoyed the benefit of a hard-won system that for the most part looked after them. Things were fair, people who had responsibility for sections of the world working well took them seriously, mostly people were competent and honest about what they could do and what was going on. During that time, there wasn't a lot of antivax.

It's not real surprising that now after 30 years or so of everything being unfair, shitty, and dishonest, people react skeptically to stuff that comes out of the system. Most people don't have the education or the time and attention to distinguish what's still real honest science / medicine and what's just a bunch of cackling self-serving bullshit. I actually don't think it's fair to blame the people who don't trust vaccines. You can blame the people who make anti-vaccine propaganda, but even then, I think we should be blaming the people who created so much fertile ground of "yo we're getting fucked and everyone's lying," to the point that one idiot on Youtube can convince 50,000 people that the vaccine is going to make them magnetic.