Because the logistics won't allow for it. Every team making the playoffs in 2020 was prescient because of the inherent unpredictability, but under normal circumstances, you'd have to start the season around August 5th if every team were to make the playoffs. You want to watch a game in those temps? I sure don't.
And by week 11, many kids are just ready to be done. My senior year, my team went 6-4, had some high-quality wins, and qualified for the playoffs as a 7-seed, but we all knew we would get smoked by the 2-seed and effectively quit before the game started. If a team like THAT is ready to hang it up, can you imagine how these 2-8/1-9 teams feel?
And in the past, making the playoffs was an accomplishment and meant you had a good season. Now, it's more reflective of the 'participation trophy' problem. Other sports should revert to how football has done things; not the other way around.