I think it's a few things - one being that teams genuinely are running and operating out of play-action/max protect more, particularly on early downs, and defenses are kinda falling into that ebb and flow (not firing out of the blocks as hard on 1st/2nd down).
Third down bothers me more. I always appreciated the way DA schemed for pressure generation, but this year--so far--it seems to be far less pressure scheming and more coverage scheming. I think I saw 2, MAYBE 3, pressures in the first half (5 or more defenders rushing the QB). One was Tyrann Mathieu on a delayed blitz and the other was Pete Werner. There was very going on with the DL, pass rush game-wise, and in general guys just aren't challenging the opposing OLs schematically or technically.
This could be due to a change in philosophy. Focusing on limiting big plays vs. being aggressive and getting after the QB. The 3rd down stuff is by far the most frustrating.