Lots of subjectivity and bias built into the system.

Preseason rankings give an unfair advantage to many teams and conferences. I don't think it is a question that the SEC is the best football conference but the process is also built to favor them. If 7 SEC teams start the season in the preseason top 25 than they just end up playing musical chairs without removing the seats. Almost the same exact thing is happening or every other conference. If there were 30 games, like in basketball, than the impact is practically nothing but with a very small playoff and only 12 season games the impact is pretty heavy.