Subject matter? LolRegardless of how popular GOT was, it was an expensive show.
5 seasons is a good run for a prestige series. It's usually about that time that the writing quality becomes difficult to maintain. I'm fine with Boardwalk ending after 5 seasons. What I'm not fine with is replacing it with shows like Vinyl. It was a good production but I don't care for the subject matter at all, and apparently other people didn't either.