IMO, confidence is not something that precedes positive interactions with others, but a result of them. Attractiveness has been proven to play a crucial role in getting good grades, getting job interviews, just generally getting what you want. This applies even in situations where there is no confidence, like when people only have photos to go on, or in experiments where people are asking others for help of some kind and try to appear sympathetic, rather than confident.

This is called the halo effect. It works for all situations in life, not just dating. People with better bone structure are granted a bunch of other positive traits based on it, whether there's a reason to or not. I'm guessing it's probably because when we evolved, before modern medicine, physical health could make or break you in a lot of ways. In modern days, medicine can compensate, so that now you don't need to be born with great health in order to do well by society, however our subconscious minds failed to keep up with the progress.