Such a good insight. Did something happen?

That can be a major issue for towel bars too. If they're positioned such that someone might grab them to get up out of the bath or up from the toilet, it's better to anchor sturdy versions to studs so that someone doesn't grab and injure themselves when it rips out of the wall.

No fortunately nothing happened, but I did notice myself reaching for the bar when I was washing my feet only to find it moved unexpectedly.

Good tip. When I redid my bathroom, I made certain that the towel bars were actually grab bars attached to blocks in the wall. I can't think of a way to do that on a shower door, though.

It's not just the swinging door it's the force could bring the entire door on top of you depending on the size of the person.