Why are so many people born gay?

I've heard that 1 in 10 people are born gay, and from an evolutionary aspect this just doesn't seem right. 10% of all births means A LOT of gay people. Since there's no evolutionary advantage to being gay since you won't reproduce, why are so many people born this way? It's obviously not because gay people are ping on their genes. So what is it? Is the statistic off? Are some of these 10% actually people who CHOSE to be gay, not born that way?