No conspiracy theory here, there's nothing sure, but we can't rule it out completely either.
Just because a President, or any man, is bad, doesn't automatically mean that every word he says is wrong. And if he really is that bad, why is it necessary to fabricate studies out of thin air in order to discredit something he said, complete with people dying because they couldn't get a medication that might have helped. If he is actually bad, the actual facts should be plenty to demonstrate it.
This doesn't even seem like a "conspiracy theory" to me. If you want to get into conspiracy theories, you'd have to start asking what else is getting this treatment.
https://blogs.sciencemag.org/pipeline/archives/2020/06/02/su...
To answer your question, there can be an economic interest in claiming a competitor treatment (which is generic and manufactured cheaply) doesn't work.