Having a top 25 at the beginning of the season is absurd, and every season roughly half of the preseason top 25 does not end up in the final top 25. The main reason for that obviously is that people can not see into the future. Common sense says that the rankings should not be done before the halfway point, which is where we are at now.
Another related problem is that even the rankings at the halfway point of the season are done by what voters think they know, rather than what they actually know.