It is a conspiracy thing. Left or right wing conspiracy-minded people adopt it. Some people replace vaccines with "faith healing", others replace it with new-age shit.
Try lack of trust, or distrust in authority, it sounds better than conspiracy. Some replace vaccines with fear of disease, and anger at the lack of a trustworthy gov't.
And possibly rumors of additives to vaccines (adjuvant - Squalene, Mercury, etc.)
I have been made aware anecdotally how may times profit is chosen over safety when critical decisions are made... It has lead me to question some decision makers about the actual priorities for their decisions...