Because it's the same stupid question you keep asking. You simply don't understand science and never will. Biden is simply repeating what many scientific experts are saying (and he's quoting the well-respected IHME models here, which said ~65K lives could be saved from here through Nov with 95% masking), which is what we want our leaders to do, rather than ignoring scientific experts. Have you ever read any of the links many of us have provided on the effectiveness of masks? Do I need to repost them?
And for the 100th time, Fauci never said masks were worthless. Back in March, he said they should be worn by infected people to prevent them from infecting others and he also said they're very important for high risk people, like health care workers to have to reduce their chances to become infected.
The area he was wrong on was in saying everyone didn't need to wear them, as he was likely underestimating asymptomatic/pre-symptomatic transmission (the data were not nearly as strong on these routes back then) and also wanting to avoid health care workers not having access to masks because healthy people might use them up, since the Administration didn't do much to procure the level of PPE we needed.
By early April he and the CDC supported full masking, but yes that delay likely cost thousands of lives, although there's nothing we can do about that now, and I have no idea what this has to do with people still refusing to believe masks offer good (but not perfect) protection and refusing to wear masks when social distancing can't be assured.