how do you think they came up with the whole horse dewormer covid thing

They're full of anti-vax conspiracy nuts trying to sucker people into their MLMs as well

How do they come up with this garbage?

people will pay in both cash and attention for the feeling that they know something that ThE NorMieS don't know. Especially when it comes to medicine, where people are desperate for treatments that a) work and b) are affordable. Once they're in the group, they get buckets of social approval for agreeing with and going beyond what the group already believes (this is how echo chambers form and radicalize), they get even more social approval for isolating themselves from the non-believers, and if they go against the grain of the group after they've isolated themselves they're completely alone. The presumption that everyone who falls for stuff like this is just an idiot is part of how it perpetuates.