I think this is the answer. Both your points are two aspects of the same idea. It's something for old people because old people have the maturity needed to be comfortable with their own body in public. Younger generations are victim of the fake beauty standards promoted by social networks and maybe porn and are a lot more self conscious. Online nudity is filtered, fake, staged, edited... when you go to a nude beach there are no filters, no perfect lighting, no make up, just the bright sun that highlights all your imperfections for all to see.