Sadly, this site and the internet itself attracts a certain introverted cateory of people who make up the majority of its users. Many of whom, like creating their own internet persona of something they aspire to be. Others will be using it to try and get attention while a few will just do it to troll.
I personally don't have any photos on my profile in case someone I know could recognise me.
so that they will gain attention from hot or cute girls because they think that girls will either not want to talk to them or not be attracted to them so they choose the easy rout.
I guess they want people to think they're good looking. Maybe they want e-booty. A lot of people don't put their pictures up here, maybe some people feel that if someone knew what they really looked like, askers wouldn't consider their advice as much.
That's honestly a good question, considering I've never had the urge to do that. I would not consider my profile picture fake...
Possibly it's some sort of scheme to get positive attention, though. There's a psychological factor that "people are kinder towards more attractive people", although the term 'attractive' is subjective as it is, so this is too general to easily apply it, I guess.
They hope to convince girls that its actually them and then get nude pictures from the girls. I don't understand it personally, your on the internet ffs, its not like pictures of women naked are hard to come by!