All about self-importance: "others are there to serve me".
Carry-on luggage is usually specifically limited to ~ 7kgs, yet how often do you see people struggling to get 20-25kgs bags into the overhead locker ?
If these people were abusive to staff and caused flight delay inconveniencing others then they will presumably be black-listed by the airline.
A per-kilo excess luggage charge should also be collected. Maybe this way they will learn some manners.