I think there's a few factors to that. All the behind the scenes McGuffins aside they've set themselves 13 episodes for the last 2 series. No doubt they had it all storyboarded out. Dany threatening Varys about the next betrayal, burning the Tarly's etc - all meant to foreshadow her going loopy. 20 episodes may have seemed too much back then when plotting out what was left - all the multitude of plot points have now converged into a couple now all the major characters are in two locations. We can no longer pop over to Bravos to see what Arya is up to, Dany in Mereen, Bronn and Jaime in Dorne (now, that was ****) etc. As a result we're just getting one major plot point one after another with little exposition. The writing itself is fine.