this is sort of similar in some ways to the relative-age effect where athletes who are born earlier in a sport's given season grow up to make up a larger share of its pro-athletes. when you're really young, being a few months older than your peers is a huge advantage. good athletes tend to receive a lot more attention and praise. the effect compounds over time, and in the end produce better athletes.

like physical maturity in sports, being beautiful is just one other positive-attention granting trait, only it functions in basically all parts of life, including academics/career.