The problem with that is when you're treated with two things, how do you know what worked? Monoclonal antibodies are pretty much accepted as effective (even if they're not necessarily available everywhere) so it's easy for some to say that's what cured him.
FDA, WHO, and others seem to be resting on the peer-reviewed studies that have extrapolated that it would require large (toxic) doses of Ivermectin to have an effect. They're discounting the multitude of small, observational studies that show it works at lower levels. Curious how the same sort of studies they rely on to support some positions are considered inadequate to support others. The reluctance to approve it widely also seems to be about making sure there's enough to treat roundworms and scabies (sorry you might die, but we want to make sure this other guy doesn't get itchy).
Not saying that people should be taking the horse dewormer tabs either, those are obviously doses that are too high. But I don't see the harm in trying it on a larger scale to see if the indications from the small studies hold up.