For me, a fairly simple guidance would be: "always maintain 6 feet of distance from any other person in public (indoors or outdoors) and when you're in a situation where you can't be sure of maintaining that distance, then wear a mask." The problem is that even that subtlety is lost on a decent fraction of people, so officials then come out with these "mandatory" mask policies for everyone outside the home, as that's simply easier to remember/enforce. But it pisses people off who know the difference. I wear a mask in any store, but not walking around the neighborhood, but I would wear one if walking in a city where it's a lot more crowded (haven't actually done that yet).
Furthermore, what I wrote has a number of "exceptions" to it, in reality. For example distancing with no mask is likely very effective beyond 4-5' indoors and probably beyond 2-3' outdoors, where "contact" time is only a few seconds (since infection is dose-dependent although we don't know the exact dose for the giver/receiver and individuals vary) and someone isn't sneezing, coughing or breathing very heavily, like simply walking by someone. It's why I think eating outdoors without a mask with several feet of distance is likely fine (as long as the mask goes on when talking to anyone nearby, including staff), but that same distance might not be ok indoors with less air movement. The risk there can also be, what if someone at the next table 4 feet from me starts coughing or sneezing right at me, unexpectedly - it's risks like that which have prevented us from going anywhere in public near people w/o a mask.
So, being on the beach w/o a mask or just walking around where population density is low w/o a mask are likely very safe, but standing in line for 10 minutes within a couple of feet of someone or standing next to someone at a concert (even outdoors) for awhile are very likely not safe without a mask. And I could write out a bunch more scenarios (different businesses for example) with subtle differences from these - the list of exposure/transmission variables (and risk tolerance variability) is huge and writing a guidance that tries to include more than a few gets very unwieldy quickly. Do you see how difficult it could become to write a realistic guidance for people to follow? That's why very simplistic guidances appeal to public health officials.
