I just think idiots in more developed countries have lost respect for the diseases that used to ravage the population. Smallpox, measles, and polio happened before their time and they assume their deadliness was overstated. In an attempt to look smart and persecuted they became vocal supporters of the antivax movement. I'll admit there are probably a few of people who are afraid of needles to be in the antivaxer's ranks though.

The phenomenon doesn't seem too different from flat earthers who refuse to acknowledge objective evidence that runs counter to their beliefs and double down whenever they're forced to see the truth.