Most Helpful Guy
Most Helpful Girl
Because of basic economic principles. Namely, supply and demand.
The more demand there is for an item (or, rather, the more demand people BELIEVE there is), the more valuable the supply, and so the prices go up.
A man posting pictures of himself with attractive females is making it look like he (the supply) is in demand. Which inadvertently increases the demand. Or that's the idea, anyway.2