I think I understand what's going on....
In the beginning, McCutchen and Cabrera seemed to storm ahead of the rest. The thing is, I believe the majority of voters for Miggy were non-Tigers fans who thought he was most deserving of cover, and so voted for him (his numbers show he was most deserving, most non-team fans agree, or at least I do). However, because these people may not have been as passionate, they may have voted only one time (or not at all). So eventually, he was due to fall down.
Meanwhile, McCutchen had a great season and a great personality, while CC has a massive fan base behind him, so fans probably wanted their player on the cover more desperately. I expect these 2 to be running away with the vote