Perhaps people need to feel special, smarter than the rest. Rather than doing actual study and research (which is work) they grab hold of anything they hear that gives the appearance of having "inside knowledge" that others don't know or accept.
The beginning of indoctrination in the JW cult involves "study" of "inside knowledge" about the bible and a collection of troovz that other people don't know or accept. Rather than doing actual study and research, they get spoon fed a collection of lies that gives them a feeling of being special, smarter, and having an imaginary relationship with a Bronze Age desert god.
Certainly, there are plenty of religions, conspiracy theories, etc. that claim to be "the truth". So it's not that people deliberately choose lies. They want answers to hard questions and can't deal with there not being an easy answer. I think they want to pick "the truth" that is easy for them to stomach and gives them a feeling of being especially smart.
What causes autism? Well, we need an easy answer. Blaming it on witches would be too 18th century, so they'll go with blaming it on vaccines. Doesn't that sound a lot more scientific and 21st century? ... well, except for the fact that real scientific research proves that vaccines don't cause autism.