Those were the #2 and #4 teams in the league in offensive points per game during the regular season.
https://www.teamrankings.com/nfl/stat/points-per-game
I suppose it is possible that even though they had proven elite all throughout the season, they got to this point and both just totally stunk the joint up. The disjointed nature of the game with the extended breaks could certainly do that to a team, especially one on that stage for the first time. However, it seems much more likely that they ran into two defenses that were playing at high levels.
While the Rams were
underwhelming on defense this year compared to expectations, some of that was due to injuries (Talib missed most of the season, was healthy and available for playoffs). They were certainly expected to be a dominant defense before the season, and without a doubt they have elite talent on the DL. They were also #7 in the league in takeaways during the season.
New England is pretty much always a top 10 defense regardless of talent (#6 this year in ppg and pt/play). And if you don't think Belichek knows a thing or two about designing an opponent-specific game-plan, you have not been paying close attention for the past 2 decades.
I enjoyed the game, I thought there were some terrific defenses plays made both ways. The Rams probably underperformed due to being in that setting for the first time, but the Patriots also had a lot to do with that. I just felt it was compelling right until the end (now, if they can just find a way to cut out about 60 minutes of dead time during the game).