An additional problem (maybe the biggest problem imho) is Amazon and Netflix et al refusing to give them more than 8 episodes per season. For things with a huge amount of source material (e.g. Wheel of Time) this forces the writers to make big changes in order to try to tell a big story in a too short amount of time. Combine this with inexperienced writers or writers who think they can do a better job than the source material, and you've got a recipe for failure, in my opinion.

The Wheel of Time, for example, had many small moments that were amazing, almost perfect, but overall the show ends up being disappointing when so many other parts fail completely.