Putting aside the knee-jerk response of "of course a mask that covers your disease holes is protection against giving other people your disease"...

https://www.sciencedirect.com/science/article/pii/S120197121... (2016) on the role of (incidental) face coverings to prevent population-level disease at large gatherings.

https://www.sciencedaily.com/releases/2019/09/190903134732.h... (2019) on the role of personal protective equipment on stopping contraction of respiratory disease (flu).

And to top it off: https://academic.oup.com/cid/article/65/11/1934/4068747 (2017) meta-analysis, including a controlled section on effectiveness on population face mask use to prevent the spread of SARS-CoV.

We had the evidence.

Dr Fauci has said their initial stance on masks was to ensure that masks were available for health care workers[0]. He did not say their stance changed due to new evidence.

[0] https://townhall.com/tipsheet/leahbarkoukis/2020/06/17/fauci...

No, they pretty much lied. The CDC was for example recommending n95 usage for medical personnel and surgical masks for infected people during the first SARS outbreak.

Fauci admitted they lied because they knew there was a mask shortage, and they wanted to make sure medical personnel could get masks before the general population bought them all.