When the experts don't even agree, and have flip flopped on key stances all the same, what does it matter? The President runs the country, not Dr. Fauci. If you'll notice, all those other nations who have been listening to the experts, haven't exactly made much progress either. It's almost like there's not a perfect solution, or something...
That said, I do think Trump missed an opportunity to promote masks when it became clear that it was a decent safeguard. I don't think it would've been a big deal if he had implemented a mandate on masks, or recommended it at least. I think most just don't want lock downs, and if masks were the thing that allowed the country to operate at a fairly normal level, I don't think many would have an issue.