Because in order to end a debate and quantify what "proper research" is, you have to have rules for the debate and establish in advance what proof is enough.
In the eyes of the world governments, the debate is already over. There isn't clear evidence that it works. There's also a straightforward answer already. Whether you believe this is because they're subservient to Big Pharma or because they actually are looking at the science, they're certainly acting as if they've seen all the data they need to see.
In the eyes of the ivermectin proponents, they just need to do the right study. The debate won't be over until it shows the answer they're looking for.
Nobody is saying, "If I see this evidence, I'll believe it; if I see that evidence, I'll believe the opposite." This is basic grade-school-simplified-scientific-method science. You're supposed to define a hypothesis, design an experiment, and then stick to what the experiment shows. But here, some have already finished their experiment, and others just want to keep running experiments.
(And no, it's not a cheap preventive treatment. Ivermectin tablets cost a couple of dollars per tablet. That adds up to be far more expensive than the vaccines. It would be a cheap reactive treatment, but even assuming it works, if you're not using it as a preventive treatment, you're letting people get awfully sick and spread the disease around, it's just that they can get out of the hospital reliably. That's not a solution.)