Just observations and I spend more time in the US flying that anywhere else really.

I generally just keep to myself.

Yes, I sometimes think "she's hot / gorgeous / beautiful" etc. and want to chat to her, my English accent perhaps making her swoon, but I don't. I expect things aren't quite like Hollywood movies.
Sometimes people may be lonely, unsure of things and would be happy chatting to pass time. Sure many of us pass up opportunities being afraid of rejection and/or being labelled a pervert, weirdo or whatever.

That said, on a recent LAX-PDX flight, a man and a woman started chatting to each other (not sure who or what started it), but they got on really well and did swap numbers.