That's because females are insecure & needy. Nearly all, especially hot ones who have been pampered and spoiled their entire life, always has to have someone and fear being alone.
The good thing is that many will cheat or breakup when something else/better comes along because deep down they aren't content with their current boyfriend....they just have to be with someone as mention before.
Personally I dispise chicks like that because they are the ones who are a pain in the ass sooner or later, but they can be had...easily.
I'd take the down to earth, appreciative girl who doesn't have the "Princess" mentality, even if that means sacrificing looks a little, if I were seeking a relationship. Looks will fade with any female anyways so why not be happy, stress free, and drama free as much as possible?