I would not do that because I am not an idiot, I don't want to give out the chance someone is going to copy or download any pics of me like that. Well the girls that you do know who post pictures like that they're either 1 insecure about their body so they show more skin to get more likes and compliments so they can feel that everybody loves them 2 proud of their body so they show it off. The answer is simple. They want attention, they seek attention, they crave and yearn for it, attention is what drives them. But like at home or a public place? It doesn't make them stupid, but there's no sense in trying to play unique snowflake online when half of the male population responds to attention seeking girls. But guys fap to us anyway so I might as well profit.
It's a vicarious thrill, lurid behavior done in the safety envelope that is the internet.
The answer is simple. Coming from a guy, I don't think I would be comfortable with posting pics like these if I were a girl. Only the third paragraph applies to this question. Their body, something they can actually control. I never thought attention means that much to girls lol. I never met them, nor I will meet them.