An excellent question that shouldn't be downvoted. Why is Bill Gates "the guy?" Don't read that in a conspiratorial sense, just in a rational "can someone explain this to me" sense.
Thus questions regarding a contemporary infectious disease potentially treated by a disease causing odd politicized conspiratorial behavior on social media is right up his wheelhouse and he's a well known public speaker. There are many epidemiologists you could hear from, and most people have heard from them repeatedly, but Gates offers a fresh perspective due to his fairly unique experience and perspective.