Tinfoil hat a bit but, I think Ohio State threw the Michigan game.
With a loss in Big 10 they would have likely still been where they ended up, but without playing in the Big 10 title game they gained an extra week and also gained more footage on Oregon.
Something changed majorly in those 3 weeks between November 30th and December 21st. Hosting a playoff game was more $$$ to the school, playing an extra game in the playoffs was more $$$ to the school and then obviously winning it all was more $$$ to the school.
Beating Michigan and losing in championship game means at best the 5 seed and still hosting anyway BUT less time to implement new plays/schemes etc. winning the big 10 championship might have been an "easier" path but was also less in their control. They would have had to beat Oregon without implementing anything new and then even though they would have had a month to prepare for playoffs (had they won) there was the distraction of Christmas break.
Not to mention the noise losing to Michigan created to help use for motivation for the players.