I suspect mask wearing increases social distancing. That would explain much of the data but satisfy neither political party.
There is also precedence for some of these statistics with Asian countries during the SARS pandemic, and in these places rule following is generally much better.
And with a smaller sample size there are some case studies from restaurant transmission. Staff seem to get infected less frequently than other diners, even though they are in the space for longer. There are a few possible explanations, but the fact that staff don't take their masks off is a pretty compelling one.
IMO that’s the least compelling reason. One big one would be the staff having way more contacts and thus higher exposure to the other circulating hCoVs as well as SARS-2 itself.
The evidence for face masks is weak at best. In my opinion they don’t even make sense theoretically unless you pretend that droplet transmission is the dominant transmission mode, which is completely unproven yet widely believed dogma (go figure)
I'm also not sure why you would assume staff have had more contacts. The people that were eating at indoor restaurants in the middle of the pandemic were unlikely the type to be limiting their contacts. Most case studies also checked for antibodies after the fact, not just active COVID testing, so prior immunity would have been detected.