I think it’s likely that ‘conservatives’ (and New Age enthusiasts, and others) wanted to hear anti-elitist messages, messages that discredited experts, which anti-vax messaging is congruent with.
As a bonus, you can then get the enemy country to think the pandemic is brought by immigrants, or was invented by its own internal enemies, as a way of pushing for civil war or at least continuous, aggrieved, domestic terrorism. The pandemic has all kinds of uses if you control the discourse and can find something to blame. It becomes a natural disaster or some kind of pervasive biological weapon that you don't even have to deploy… just foster and nurture.