This isn't a professional sport where we generally have years of data to go with. CFB has 4 or 5 years on any given player at most but usually 1 or 2. Coaches make a big difference. Incoming freshmen and transfers can make a huge difference. Throw in injuries and other things and there really isn't much to go on over the course of a 12 games season. So, to compensate, they, like the human polls, use things like what happened last year to seed the rankings. The problem is, last year is irrelevant. Otherwise, may as well just crown Alabama and be done with it.
This is why the CFP is dumb. There is too small of a sample size to make a judgement on the best 4 teams over the course of 12 games.