Time was the issue. They ran out of time waiting for GRM, so they went their own way. If they had waited... We'd still be waiting, but wouldn't have gotten the suck.
You mean if they’d been competent show runners in the first place.
The show was great when it was based off of good writing.
Then it got sketchy as they had to rely on GRRM’s notes.
Then the notes got more vague, and season 7 and 8 turned into garbage.
Conclusion: D&D were mediocre show runners who couldn’t hire competent writers, and thought game of thrones was about subverting expectations instead of strong character arcs.
Justifiably, it lost them their next gig.
HBO was willing to wait for good seasons. But D&D wanted to get into a Star Wars contract with Disney. They rushed season 8 out the door with lazy writing to get that Star Wars deal.
After season 8 traumatized GOT fans and bombed in reviews, Disney backed out of the deal, and D&D have fallen into obscurity.