I have a feeling George R R Martin told them
"Dany goes mad queen and burns down King's Landing. Jon kills Dany. Jon ends up North of the Wall. Bran ends up King"... and then they proceeded to fill in the blanks horribly.
On some level, I feel for them. Obviously George R R Martin can't even figure out how to get to that end point. But man, they blew it.
Bran: Not fulfilling, because they never found the character interesting. Flat out avoided him for a whole season. Dipped their toes in the 3 Eyed Raven thing, but ultimately skated around it, because the fantasy element of the show always perplexed them. They spent the last couple seasons just having him sit there acting like a weirdo consistently saying how he's "not a man" anymore - only to turn around go "hehe, just kidding guys I always knew I'd be King" - which is doubly upsetting because it means he sat by doing nothing while thousands died because like everyone else he had a boner for the Iron Throne.
Jon: The entire story is about him. He's the core arc of this entire endeavor. I've been saying this all along. He can choose to turn down the Throne in favor of living North of the Wall, but that needs to be communicated by him. Leaving his fate to some randos who weirdly ignore what they know about his heritage was completely illogical. That above all things leaves the biggest empty feeling about this conclusion. It doesn't feel complete.
Dany: I care less about this, because she's always been a mass-murdering nutjob to me, but I get how fans would be upset. From what I understand, in the books she's a bit more of a looneytoon from the beginning... breast feeding her dragons and having weird hallucinations and things like that. So really, my guess is the writers just never fully understood this character, leaned into her savior persona, and then scrambled to reverse course too late.