Supposedly HBO are reluctant because they think it could hurt their subscribers, but yeah if someone is only interested in watching GOT say then they're most likely just not going to pay the subscription fee, they're going to look for it online. Ditto with international viewers who physically can't get that channel. They may as well make some money on the streaming rights from it and increase their fanbase, but the people in charge always seem so much more concerned with the bottom line and losing money, and it's the viewers who lose out