It sows distrust in authority, so that those people will listen to fringe voices. These fringe voices tend to be grifters, scamming the rubes.
Politically it’s a binary issue, no room for compromise. If you’re anti-vax, you’re voting for the Republican candidate, despite what the other guy might be offering. So, this locks in votes and also plays into the long term strategy of having an uneducated underclass incapable of critical thinking. This provides cannon fodder for the politicians, and low paid drones for the fat cats.