It's kind of like some people have a friend that they brag to I call it a bragging friend where you only talk to them when you have something to brag about and I feel some users use this website only to brag but they disguise it in the form of a question
Like humble questions? I don't see it very often. All I can think of are the really pretty people being like" am I Ugly? :C" so in those cases I feel like the person just needs attention more than anything else. It doesn't really matter to them how they get it as long as they do.
Because they are looking for approval. Probably suffering from low self esteem. It's the same as those girls who take topless pictures of themselves and stick them on Facebook asking guys "do you think I'm hot?".