Maybe they don't have TVs/cable?
My GF is completely addicted to Game of Thrones, but she openly admits she will not pay $540/year for basically a single season of a show.
All the "but look at all the other content you get" arguments are null, if I were interested in any of that other content, I'd already be paying for it. But we're not.
She can torrent it now and watch it when she likes for free. While she will undoubtedly go buy the DVDs when they're released (she always does), the incentive to watch it "now" as it's being broadcast is worth some amount of money $0<n<$540 for her.
I really don't buy the argument that HBOGo wouldn't make any money if they charged $15/mo for streaming-only access. Nearly everyone I know (none of whom have cable/satellite and HBO now) would gladly pay that price or even marginally higher.