> Nothing about masks or the virus or "the science" changed.
Are you sure? Because I'm pretty sure they refined the transmission model after understanding the virus better, looked at the cost / benefit ratios on mitigation options, and concluded that masks were better than nothing given that quarantining everyone wasn't an option.
In that sense, "the science changed" in that we understood the situation better. There is also, of course, the gap between policy and science; the science can say X is true, whether we do Y in response to X being true is a cost / benefit calculus, and that calculus was changing continuously as policymakers updated economic impact estimates and saw how people responded to different approaches.