That’s a good question. When he wrote the first book in the series, I think he wanted to have a continuing series but wasn’t thinking of any sort of ending. And I don’t think he was thinking of HBO at the time that he wrote it, he was just thinking of the publisher giving a forward on the next book in the series.
I don’t fault George R. R. Martin, he’s not as bad as J. J. Abrams who comes up with good beginnings, but has no clue which way the story is going to go, much less if there is to be some sort of finale the story is building to. Neither are J. Michael Straczynski in that regard.
That’s also a good question to ask, since the Hollywood machine has been around long enough that it has evolved. Its roots are in the “come back next Saturday for the next exciting episode!” era, but also from later, where syndication demanded the episodes did not need to be shown in order, and then the home video era of buying entire seasons as box sets, and now the streaming services era where viewers demand entire seasons.
I think the real problem lies in stories that keep promising that everything is building to some sort of giant climax, and then moving it ever further into the next book, the next season, and denying us release. Eventually we get tired of constantly being teased.
I think fantasy authors get a pass on this, because the genre has always been about multi-book epics. That’s its whole jam, pretty much following the pattern set by Tolkien. Fans expect it and want it. Enormous world building spanning multiple books is arguably necessary to the genre*.
What’s new and exhausting is that everything is trying to be like that now. You can’t just have a good story that wraps up anymore.
*There are exceptions of course. There was a series of Dragonlance short story anthologies that were really excellent self contained small fantasy stories. They were sorta cheating though because the Dragonlance setting already existed and had been built up by many other books and games
This exact reason is why I’ve loved Last of Us. Every episode (for the most part) starts and finishes a conflict in the same episode. It’s been SO refreshing to watch. I can’t take the cliffhanger TV anymore.