A better example is drinking. Say a study clearly shows that low social economic status people drink twice as much alcohol as other people. This doesn't show that being low social economic status causes people to drink more. But regardless of that, if you wanted to date people who drank less alcohol, on average by dating only people of non-low SES you'd be dating people who drank half as much compared to if you only dated people of low SES.

I.e. if A is a reliable predictor of B, it doesn't matter whether A caused B or both A and B are caused by some other factor; A is still a reliable predictor regardless.