I think it's because the threat is not visible. In the 50s, 60s, 70s, and 80s, diseases like polio, measles, mumps, etc were very common. Everyone knew people

I think it's because the threat is not visible. In the 50s, 60s, 70s, and 80s, diseases like polio, measles, mumps, etc were very common. Everyone knew people who had them, knew how awful they were, and vaccines were a clear way of solving this imminent and pressing issue. I'm 30, and I've never had any of those. I've never even seen a case of measles in anyone I know. I'm obviously still going to vaccinate my children, but the benefit is not immediately obvious. They are very unlikely to get measles no matter what I do.