While your local authorities may have voiced such a recommendation for people to follow, as far as I know, no country which has mandated mask usage, is requirin

While your local authorities may have voiced such a recommendation for people to follow, as far as I know, no country which has mandated mask usage, is requiring specific behavior around the donning and doffing of that mask. (Please point to specific legislation if this really is the case where you are.) If there is no requirement and enforcement mechanism around a certain behaviour, then IMHO it is excessive for any of us here to complain that the general public is not observing that behaviour. We can only expect the general public to observe any restrictions to the least possible degree; only if there is a hard rule that is being enforced will society overall heed it. Public-health authorities generally know this, and so if they are not pushing for certain behavior to be actively enforced, then that behavior likely matters less to curve-flattening efforts than you might assume.