I don’t know if you are following it but Warner isn’t in the best financial state and a Jon Snow show isn’t going to drive additional subscribers that it doesn’t already have with HOD.
The new guys in charge are super cost cutting oriented that is why you saw several movie releases shuttered and you are seeing HBO shows streaming on Netflix for the first time.
They had a target goal of cutting 3 billion in cost when they merged with Discovery and they cut 5 billion. Right now economics are making all the decisions and they don’t need this project.
That could change down the road but it’s the reality now.