First..McVay is an elite coach!! ... but...
Second... Rams should have gone for it on .. what was it? Fourth and 14 or so mid-field with 4 minutes (appx) to go.
Here's why...
1. The one outcome that ends the game in Detroits favor is for Detroit to get the ball and get a first down. Game over.
2. If the Rams go for it on fourth down near midfield, and don't make it, that's basically the same situation as them punting on fourth down. In EITHER case, you have to stop Detroit from getting a first down. Field position is NOT an important variable in this decision -- this makes it an unusual situation and counter-intuitive decision. This is a key point. I don't care if the Lions get the ball on their 10 yards line, or the 50 yard line. In either case, if they get a first down (much less two of them), game over. Do NOT just hand them the ball, fourth and long, or not.
3. Despite it being fourth down, the one outcome that puts the Rams in a very favorable situation is for them to get a first down. Even if low probability (and it's not that low last night), this is the one outcome on the down that really favors the Rams. But punting, that outcome is eliminated.
4. Another small factor is the quality of the defense. This is not a huge factor unless the defense is the '85 bears. But as a minor variable to consider; the Rams aren't exactly the team to bet on to stop Detroit from getting a first down. The defense was playing much better, but in any case, the quality of the defense may matter, but the heart this decision are points 1-3 above.
Don't you love it?