I read recently from one of the companies that specializes in media industry research that HBO gets, on average, about $7.75 per month for each customer who subscribes through a traditional distribution partner (cable, satellite or telco MVPD). (I don't recall the exact figure but it was somewhere in the $7.60 - 7.90 range.) That's the wholesale rate that HBO charges Comcast, Charter, etc. and then the cable company sets the price they actually charge their customers. While a lot of operators used to charge a little more, maybe $16 to $18/mo, it seems like about everyone has pulled that down now to $15/mo to match HBO's direct-to-consumer pricing for HBO Now. That's also what Amazon, Roku and Apple charge to subscribe to HBO as a streaming channel through their own apps.
If you sign up for HBO Now directly through the HBO Now website and they handle the billing, then they're getting the full $15/mo. If you sign up for HBO Now inside the app you downloaded from an app store operated by Apple, Google, Roku or Amazon, then that company handles the billing and they take, I think, about a 20% cut of the $15, leaving $12 for HBO. Either way, with HBO Now, HBO is bearing all the operational costs of encoding the streams, running the servers and paying for the bandwidth to deliver the streams.
If you sign up for HBO as an add-on inside another streaming app (e.g. Prime Video, Hulu, The Roku Channel, the new Apple TV app), then they handle the encoding and streaming operations as well as the billing, so they take a bigger cut. Not sure of the amount but I think I read it was ~30%. That would leave $10.50 for HBO.
Assuming all that is close to accurate, you can see why HBO would prefer folks to subscribe to them via streaming. It's more profitable. On top of that, HBO also gets lots of valuable user data when you stream rather than watch on a cable/satellite box. Streaming gives them much more accurate info about what their customers search for, what they watch, at what point they stop watching shows, etc. Netflix says that kind of user data is invaluable to them. (That said, many who get HBO through a traditional MVPD do stream HBO too, using the HBO Go app, which gives HBO user data but at the cost of providing the streams.)
And, of course, AT&T plans to transition HBO to even more of a direct competitor to Netflix this fall when they launch an expanded streaming service that will be centered on HBO content, but with lots of additional complementary content. They've said that the current standalone HBO service will continue to exist, and obviously HBO doesn't want to dump the vast majority of their customers who subscribe through traditional MVPD partners, but it seems clear that AT&T sees HBO's future as *mainly* a streaming service.
When you take all of that into consideration, is it really any surprise that AT&T is playing hardball with Dish over HBO carriage? I imagine their thinking is "If Dish customers want HBO, let them subscribe via one of the more profitable streaming options that we actually prefer. And if they live out somewhere internet service isn't available, that means their only pay TV options are Dish and DirecTV satellite. Some of those folks will ditch Dish and come to our DirecTV service so they can get HBO, which would be great because DirecTV is absolutely hemorrhaging subscribers."