https://www.cnet.com/news/game-of-thrones-season-8-likely-to-drive-hbo-now-signups-data-shows/

Second Measure looked at trends before and after previous seasons of the show to reach that conclusion.

"Roughly half of the subscriber growth from Game of Thrones season 6 vanished within three months of the finale. Our latest analysis, updated to include season 7 data, found a similar effect around the Game of Thrones premiere," Second Measure's report said.