I think the main point was to flatten the curve, as hospitals were overloaded.
Masks (at least the better ones) did reduce the likelihood of getting covid, and people didn't have the antibodies they have now.
And if you lived in a state that published open data you could see this happen — hospitalization rate goes up and bed count goes down, and we’d go to tighter restrictions until the trend reversed and the bed count went back up. A lot of the public health response wasn’t about stopping COVID transmission, it was about limiting the effect on a hospital’s ability to provide care for things like life-threatening injuries.