Quoted from vireland:
They could easily put more intrigue into it and do 2 more seasons. Problem is, they don't have the writing chops to do it well, so they're trying to get it over with.
After season 5 or 6 I watched an interview with the show creators, Dan and dave. At that time they commented how HBO wanted LOTS MORE Game of Thrones, but they were running out of steam on the project ant wanted to see the ending in 8 seasons. Not long after that we started to hear mention of “spinoffs”. Turns out that the spinoffs were in fact going into pilot production and are prequels to the story.
Quoted from bladerunner:
They DO NOT WANT TO write an end. Many prequels to come! You don't kill the goose laying gold eggs do you?
I want more!
You do understand that a prequel is BEFORE our current story, none of the same characters involved. The end has been written, but what about the beginning? The 1st prequel is going to be called The Long Night (same as the title of the last episode; #3). This could show us the fight with the first men and the children of the forest, the creation of the white walker, how they drove him back last time. It could detail the first Starks, or the creation of winterfell.
Another prequel could be the doom of Valyria. How dragons were trained and then ultimately wiped out.
How about the story’s of Duncan and egg? There’s enough for another series there.
You’ll get more.