Here's what I think it boils down to, and the guys on Husker Sports Nightly hit the nail on the head with what I've been thinking since he left.
When running backs go to a division 1 school, they think they are the best running back in the nation even if that school recruited a couple of other backs. Then, when this guy gets there, he realizes that everybody is just as talented if not more talented than he is. He then soon realizes he is going to redshirt, and before you know it he is 3rd or 4th (maybe even lower) on the depth chart behind guys who haves years to play (like him) but are playing better than he is. He starts to think the place he is at isn't right for him, so he decides to transfer to another place to play ball and get more PT.
I bet Collins just pulled himself together and realized that he didn't want to leave and that he needs to tough it out and perform. Being so far down on the depth chart that he is, he probably realized he needs to work really hard to start getting PT.
Boy, that is some really good insight. Thank you.