GOT wasn't milked. It outran the unfinished source materials and then the director/producers D&D "phoned it in" because they started working on Star Wars.
And seasons are so short that even the bad seasons weren't a lot of TV.
It does seem like they had an outline for GRRM’s planned ending, but I doubt he was just going to have all the characters join forces and become a zombie fighting show.
Plot armour, a complete lack of consequences, CGI battles over dialogue, _really poor_ writing and ridiculous plots just to get characters in the right place at the right time.
The first four seasons are among the best TV ever. The final two among the worst.
And seasons are so short that even the bad seasons weren't a lot of TV.