I sorta get the conundrum a guy like McVay has. If you've been wildly successful all year, as they had been on O, you're going to stick with what's worked until you're forced to switch gears. The problem is for both the Rams and the Chiefs by the time you consider doing something different (which Reid did but McVay didn't) the first half is already over and you're most likely already losing which limits your options.
The other thing Belichick does, which I haven't seen any other coach do, is go with a completely different game plan than anybody has seen to start the game off. That takes balls. The Cover 4 hybrid scheme between zone and man was something the Rams hadn't seen the Pats do in film all year. Similarly on O, one would have thought James White would be a significant factor as he's one of the more skilled guys on the team. I don't remember him getting into the game. If you spend hours studying how to stop short passes to James White, hey guess what - you just wasted a lot of time prepping for someone that the never ended up deploying.
He's been doing this for years. Back when they played the Eagles the first time, they sent out not a 4-3 or 3-4 Defense but a 2-5 which again they hadn't deployed all year. If your QB can't improvise (Goff) its game over.