Amen.
The redditors were a particular case of this. Most people got into the novels after watching the show. Many never read such long novels before.
That is a big investment of time.
People wrote long theory essays, many being neat ideas but not fitting with the style of the author or good story telling.
That is a big investment of time.
People read these essays, also listened to epic series about them on Youtube.
That is a big investment of time.
Show kills that stone dead with a twist, and it suggests GRRM planned something similar, or at least that plot doesn't matter in the grand scheme of things.
That is a big investment of time. That was a huge waste of time.
So ... much raging - and coping by shitting on the show. This provided the pseudo-intellectual wing of the show backlash, and had been bubbling up for years. The non-intellectual wing was simple fans of specific characters - 'stans', and people who dreamed of specific romances - 'shippers' who did not get the outcomes they needed.