Nate Silver isn't some weird Neo like figure who strides alone dispensing Truth via a college-level understanding of statistics -- his brand of analysis is not unique or even particularly remarkable save that it is rare in the mainstream media.
Too, it's a bit rich to be badmouthing sports on Hacker News, home of perhaps the most solipsistic conversations on the internet. Sports is a very important part of many people's lives; surely that alone lends it sufficient heft to be a defensible use of Silver's talent?
As for why, Silver got started in sabermetrics, and going back to working on sports stats is almost certainly because he likes it. And I imagine ESPN backed up the proverbial dump truck, too.