For some cultures and religions not wearing a head covering counts as disrespectful.
Again, for Quakers for many years it was seen as important that men should not take their hat off in the presence of a "social superior", even the king.
These are conventions that come and go and change their meanings. As indicators of bad manners or discourtesy they don't really stand up.
One thing today is that, what with shopping malls and such, it's not at all clear what counts as outdoors and indoors anyway. In the same way the existence of automatically opening doors gets people out of the habit of opening doors for other people. In spite of which, in my experience, a surprisingly large number of people, including young people, do in fact hold doors, especially for people with parcels or with children.
(On the other hand I just ran this post through a spellchecker - it didn't accept "disrespectful" and "discourtesy" as valid words...)