My thought basically boils down to this-
If you score a touchdown, the Bills need a touchdown for OT. How confident am I in a touchdown? Not at all when you consider the Ravens last scored one in the first quarter and one was gift wrapped by great position on the interception return.
Additionally, if a touchdown is the only positive outcome, what are the negatives? An interception, obviously, is one. A fumble is a huge one. A sack is a huge one. An incompletion is probably the best failure the Ravens could have hoped for. I just see too many possible scenarios for what could go wrong, and obviously it did go wrong.
If you get a field goal, the Bills need a field goal for OT or a touchdown to win. Given the Ravens are up, the Bills can't afford to risk milking the clock and attempt to score a touchdown- they need to take touchdown opportunities when they present themselves and that potentially gives the Ravens back the ball. Or, the Bills milk the clock and settle for OT.
Do I trust the defense to make the stop? They haven't been great, but they did just for a three and out. I probably trust them more than I trust the anemic offense. And if the Ravens go up three, this impacts the Bills playcalling and gives the Ravens a little more freedom in play calling. They can afford to be a bit more aggressive and not have to worry that any mistake they make could signal game over.
That's what would have been running through my head, personally.