I do not think everyone understands this, and I think if they did (in general understand such things) the world would look very different. Certainly those messaging do not think people understand it.
Walid Gellad is a relatively prominent Very Serious Person epidemiologist, but not one of the most known/influential, so makes sense you don’t know, but he’s one of the chorus of people doing the thing in quesiton.
I’m not sure about that. Seems like everyone gets that posted speed limits are not magic numbers such that exceeding them to any extent leads to carnage and high repair costs or that adhering to them ensure one avoids such results. The 6 foot rule is not really any different of a concept.
My experience has been that people generally give reasonable space, often erring towards more space than less where that choice is clearly possible.
Given that most people seem to get the arbitrary number is posted to give everyone some common standard to coordinate around without it being some type of exact numerical value of specific import.
As for those doing the messaging are also likely doing so based on filtered and skewed information—just a variation on the central planner problem of non-omniscience.