When a Top 25 team loses, they tend to drop anywhere from 6-10 spots early and then less as the season goes on. For teams like Boston College, SMU, and Wake Forest who are all undefeated, they have a huge uphill battle.
Teams like those mentioned above have to fight through all the teams ranked ahead of them, which in their case was at least 44 teams either ranked or receiving votes. So a team like Texas or Clemson could suffer a loss and still be ranked higher than the undefeated team.
This is especially true for teams like UTSA, Memphis or Boise State. These teams could start off the preseason completely off the radar and lose one game in their first six weeks and be done for the year. If you take out the preseason polls, maybe a team like UTSA is ranked right now and could suffer a loss and still find a way back in later.