That's what a scientist does, Win. They study the available data, and report the LATEST demonstrable findings based on that data. And as the data changes, very often so do their conclusions and recommendations. They also usually admit that the old findings are outdated, and sometimes that they are wrong.
So if Fauci said back in March that there is no reason to wear masks, and now is saying the opposite, good for him! He is showing us what a good scientist does: always testing, flexible in his conclusions, admitting when he was wrong.
My only criticism of him would be that maybe he was a little premature with that March pronouncement, as the disease was so new, and obviously not enough was known then about mask wearing. But now we do have the evidence that masks make an enormous difference. I saw on today's news that if you wear a mask outside of your home all the time, you are 70% less likely to get Covid 19!