Not sure if someone's addressed this ... but there is a further major difference between (a) ballgames and movie theaters versus (b) plains, trains, buses. And that is the volume of the spaces in question. Additionally, most football & baseball games are outdoors, but for the ones that aren't ... the volume of the domes makes a big difference. Also, domes and arenas tend to have vigorous HVAC that keeps air circulating more than what's typical in, say, an average office or home (paging
@GroveDiesel for a professional HVAC opinion).
But what about churches? Brass tacks -- churches where people sit together but don't shout out, sing, get in each other's spaces, etc. were probably really OK to attend all along. A quiet, solemn service -- no "peace be with you" or communion or post-service pot luck -- was likely always COVID-safe, especially in a large high-ceilinged church with some spacing in the pews. Around here, we have a lot of strip-mall churches that cram 60 folding chairs into an average living-room sized space with low ceilings and maybe-it-works HVAC -- a lot less COVID-safe.
Really, it's been a case-by-case evaluation requiring nuance. One-size covering rules weren't ideal, but they made more sense to most people in general and were much simpler to apply.