Many people listened because he wasn't some youtuber doing his research, he was the head of the "Infectious and Tropical Emergent Diseases Research Unit" ad the Faculty of Medicine of Marseille.
I've watched one of his interviews where he stated that people survived in his unit with hydroxychloroquine and that he had numbers to prove it.
When you look at his credentials, and my.braincells.count(), it was hard to identify it as misinformation.
But even without being knowledgeable about statistics, there were a lot of very serious people giving very good arguments against his results. You just had to see them. And seeing all the Facebook doctors lunatics instantly side with Raoult and defend him tooth and nail should definitely raise some red flags...