D&D just stopped giving a shit and wanted to be done with the show so they could move on to new things. That's why the turned down HBO's offer of doing a 2 season 20 episode finale. Turned down a 10-12 final season claiming they only needed six episodes at an hour and a half(which would be equivalent to 10 episodes) then said fuck it and only had three hour and a half episodes for a total run time of what is 7 and a half episodes.