I would suspect that he was the sacrificial lamb. After failing to make the playoffs for the first time in 6 years they had to sacrifice someone. His defense was a bit worse than the previous year. After he left the defense ranking has continued to fall. Hard to stay at #1 for that long of a period.
I am good at remembering pivotal points in time...what the thinking was and how that influenced decisions. That type of thing doesn't always show up upon backfit many months or years or decades later. It is the reason I try to mention stuff like Kenny Easley always considered superior to Ronnie Lott in college, while playing at rival schools in the same town. You aren't going to pick that up while scrambling for bios or stats, etc.
That Rams game late in 2017 really jolted the Seahawks. I was following the Rob Staton blog and another Seahawks blog. The team obviously had declined but there was still hope of a playoff berth and ongoing legitimacy. But that all came crashing down when the Rams went in there and embarrassed Seattle 42-7. The Rams were the new glamour team under McVay and Goff, etc. They were sweeping through the league but Seattle had reason to be smug because the Seahawks went into Los Angeles early in the year and shut down the Rams offense, winning 16-10 as small underdog. I remember that result being a comfort blanket among Seahawk fans for the next couple of months. Nobody can shut down the Rams but we did.
The second game was basically pick-em to Seattle a 1 point favorite. Pivotal game for both teams. Seattle could still win the division. They were 8-5 to the Rams' 9-4. As mentioned, Seattle won the first matchup so obviously they would hold the tiebreaker with a series sweep.
The game was televised in the late Sunday time slot on Fox. I watched it in Miami. The Rams were so dominant it was like a high school game with a running clock. The score was 34-0 at halftime then quickly 40-0 midway through the 3rd quarter. Keep in mind this game was played at Seattle. Gurley was waltzing into the end zone, schemed so wide open there wasn't much he had to do but laugh.
The Rams were merciful the remainder of the game.
All the fancy reasoning and rationalizing and backfitting regarding why Kris Richard was fired is conveniently ignoring that single game and how pivotal it was to Seahawk mindset. I remember the stunned silence at the stadium, and then the reactions on the Seahawks blogs. Everyone agreed that sweeping changes had to be made. They just saw the direct comparison to their new division rival, and there was no comparison. I remember even the normally calm blog owner Rob Staton saying that pretend mode had to immediately be thrown out the window, that the remaining games of the 2017 season basically meant nothing in comparison to making meaningful changes on both sides of the ball.