He played the 12th game safe knowing he's a huge favourite in rapid and blitz. Like Kasparov and Grischuk pointed out today, every other chess player gets worse playing rapid/blitz but Carlsen is the only one who actually improves.
Under these conditions it's more than sensible to move into the terrain where you have an advantage, if thinking strategically.
I would argue the problem is that most of the fans have become conditioned to expect entertainment, drama and bold moves in sports like we see in overly dramatic movies.
But historically, if you consider generals or even have a look into Sun Tzu's art of war, the strategists and generals that were most regarded were the ones who were able to win in a manner that it seemed easy, unimpressive, without drama or heavy losses or huge risks involved.
That's what a great strategy is about taking battle where the outcome is decided beforehand. And that's what Carlsen did.
The downside is it cost him €50k as the money distribution goes to 550/450 in tiebreak from 600/400 if decided in classical.
So he exchanged a potential loss of €200k at a favourable odds for a sure loss of €50k with potential loss of €150k at a much better odds. Now here's where we could question his decision speculating what the actual odds were, but who knows if he cares about the money.
I enjoyed this final a lot.