How many seasons does Game of Thrones have?

How to get close to this number

Prestige cable dramas run five to eight seasons, and one that became a global phenomenon will be renewed to the upper end of that range rather than the lower. Eight is the answer, and it is the top of what a production of that cost and complexity can sustain.

The structural problem in the explanation is the one worth understanding: the adaptation caught up with its unfinished source material. A television schedule runs faster than a novelist, so any long adaptation of an in-progress series eventually faces a choice between stopping and inventing — and this one invented.

That is the same constraint described in the anime questions on this site, where adaptations either pad with filler or diverge from the source. The difference is that padding is available to a weekly series with cheap episodes and not to a show costing tens of millions an hour. The economics of the format determine which failure mode you get.