they are created from scratch each week - meaning they

1. Don't rank the teams based on where they project the teams will end up, and

2. Don't use the previous week's rankings as the baseline for the following week's rankings.

That being said, considering the same people are making the rankings week in and week out you can expect a certain level of consistency from week to week. But it's not that uncommon to see big moves from one week to the next and especially over the course of the season.