Maybe they couldn't get a doctor to prescribe them the human pill because of all the politicization so they took the "horse paste" version.
You seem to have first hand knowledge of all these people's situations, are you following people to the livestock supply stores or talking out of your ass from stories you read on Reddit?
Most people that I know have that have took Ivermectin were taking the human pill. Only on the internet and news media have I seen people talking about horse paste.
Also, some vet meds are okay for humans (as long as you dose correctly), yeah you shouldn't take them, but that doesn't stop some of my liberal friends I know from taking horse tranqs (ketamine).