I think it's because the threat is not visible.<p>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.<p>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.