Anecdotally, everyone I've heard say "the vaccine caused ____" are the same people who say "The fish was thiiiiiiiiiis big" and regularly blame things on made up reasons instead of being willing to look at themselves. My brother says he's "never been sicker than after getting that damn shot" which is a HILARIOUSLY BOLD FACED LIE! He was literally bedridden for several weeks this year with various illnesses and nothing after the shot, but sure enough, because he wants to believe the shot kills you, he blames made up illness on the shot.

It's no different than parents blaming their child's autism on the vaccines they got, it's not exactly a rigorous examination of the evidence. It's wishful and directed thinking.