>Those people are overpaying for the service, and that makes them more money than opening up HBO Go would.
You and HBO are assuming that the number of people who would join HBO Go without a cable subscription isn't going to be greater than the number of people who would drop cable to just get HBO Go. It's just a guess.
It's not about number of people, it's about how much money they're getting from each.
A cable subscriber is worth a lot more than an HBO Go subscriber, since they get kickbacks from the cable companies, they are cheaper to acquire, since they get a lot of free advertising through the cable companies, and they are less likely to cancel, since it's harder to cancel an entire cable package.
So it's not a 1:1 relationship between cable customers and HBO Go customers. They need to acquire several Go customers to make up for each lost cable customer. But cable is shrinking, and streaming is growing, and at some point the scales will tip. However, they have to be damn sure that it has tipped, and that they can sustain their current revenues, so they will probably be a bit cautious and conservative, and let their cable-only deal stick around a bit longer. This might not be what you want, but such is life.
(Or you could move to any Nordic country and enjoy HBO Nordic, which is HBO Go, but without the cable subscription requirement.)
You and HBO are assuming that the number of people who would join HBO Go without a cable subscription isn't going to be greater than the number of people who would drop cable to just get HBO Go. It's just a guess.