I think the issue is it's far less clean than it used to be.
Up until 2011 you were competing for a single auto-bid. That was still typically the Rose Bowl. Now you are using the tiebreaker to determine going to Indianapolis, not to the bowl game. Second, what constitutes "going to the Rose Bowl?" Is it actually playing in the Rose Bowl? Is it going as the Big Ten champ? Playing in the Rose Bowl isn't as clean as it once was. For example, look at 2015. Michigan State won the Big Ten, but went to the Cotton Bowl as part of the CFP. Iowa got the Rose Bowl as a consolation prize. So in some sort of tiebreaker where that is used, what counts? For tiebreaker purposes is MSU 2013, being the last time they played in the Rose Bowl, or is it 2015, the last time they won the conference, even though they didn't actually play in the Rose Bowl? Or 2016, where OSU didn't even go to Indy, but made the CFP, Penn State won the conference, played in the Rose Bowl, but didn't make the CFP. If we got to that tiebreaker somehow, it starts getting kind of unwieldy now. Plus longest Rose Bowl drought, when determining going to the Rose Bowl, makes sense. Longest Rose Bowl drought, to determine going to Indy, does not.