The cycles last a long time. Alabama was not good at all for about a decade during the late 90s/early 00s. Clemson's emergence was a long time coming and did not happen overnight. If you're looking for the balance of power to flip every 2-3 years, not only will that not happen but it has never happened that frequently in the history of the sport.
Clemson is an incredible example of what you are saying doesn't happen anymore. They aren't just a good team; they are a juggernaut of a program now. Better than Ohio St, better than Georgia, better than Oklahoma, better than anybody besides Alabama. They not only entered this club but have stayed there for several years now, and they did it in this era that you say is different than how it used to be, and they aren't even a traditional power. If I'm a school like Georgia or Oklahoma, I'm scratching my head and going "How in the hell did Clemson ascend into that spot and not us?"