Masks protect the wearer, but protect them best if the infected person is also wearing a mask. You know this by now.
I think at first there was hesitancy to introduce mask wearing because there was major uncertainty about how COVID was transmitted. That science did continue to evolve for several months. Fauci has also noted (and this has been mentioned on GMG previously in threads in which you participated) was that initially there was a concern that if the CDC went all in on masks at that point, there would be such a run on PPE that medical personnel would end up without a supply of PPE when regular citizens gobbled it all up. In some areas, that did happen even without a mask mandate.
I think they should have gone all-in on masks early and hesitating was a mistake. It would have taken more decisive government action to meet our supply deficit, which never really happened.