Yes, but they still get significant $$ from the operators during those months when programming is weaker. Having an OTT service would destroy that model.
The problem with people thinking HBO should offer an OTT service- has anyone thought about how many people would cancel their subscription at the of the season of Game of Thrones (then sign back up before new season)? The business would crumble..
It's when you download the title to your box. Most operators have QA gate so if there's macroblocking or audio drops, they'll contact the programmer to re-deliver.