Why do shotgun shooters choose to look the other way?
You are the one who needs to answer that, seeing as how you did nothing.
In the first two cases, I wouldn't have gotten too upset. You could clearly see the gun was broken open. Not good etiquette, but I wouldn't have said anything about it unless it happened again.
Third case, I would have spoken up immediately. If I got anything but a conciliatory response I would have walked away.
Fourth case, I would have watched him closely to see if there was any more problems with his gun or with him. If so, a gentlemanly word spoken to him about it, again if I didn't receive a humble response, then adios. He did have his gun pointed downrange, as he should.
SRH