Don't they have to shoot most of next season THIS summer?
Or they could pull a Sopranos and take 2-3 years between seasons.
They have not been having their heads up their asses like they did with Sopranos.
"It's not TV it's HBO" means that YOU are not the product. In TV you are the product and the customers arethe advertisers; on HBO you are the customer and HBO is there to serve you.
Back when the Sopranos aired we had information an synchronicity. Most people didn't know to just log into the internet and search "when is the next episode of Sopranos"; if they did, they would have canceled their HBO subscription for 2-3 years. Today, with the customer so much better informed, we can check "when is X show coming back".
And people do have tolerance limits; if they watch a show that lasts 3 months and comes on every year; and they watch one or two other shows that also last 3 months, they will not bother to cancel for the 3-6 months that they aren't really getting their value out of the service.
But when subscriptions start taking years on end to justify their presence; that's when modern subscribers start re-thinking the value propositions. True Econs, economically rational agents, would just un-subscribe every time what they want to see goes away; but that's just now how real humans work, and HBO knows it.