There’s something about a plane, or maybe it’s being away from home, that gives people license to do something they wouldn’t otherwise do in semi-public. And they can escape their usual inhibitions and talk up strangers thinking something might come of it.
However in the air, just like on the ground, giving attention to fellow passengers may be unwanted. I remember talking to a co-worker years ago about the number of times she noticed married men on planes taking off their wedding rings when they sat down next to her. She avoided Southwest Airlines because of their open seating policy, a virtual invitation for men to choose the seat beside her and make unwanted advances.