Wavering commitment to football has definitely been an issue at ND, but I'm not sure that explains most, or even much, of the rise and fall other programs. UF's commitment to football didn't suddenly decrease in 2011. The quality of their coaching did. Similarly, Stanford didn't suddenly do away with admission's requirements for football players in 2007. They simply got better coaching.
If winning big in college football were as simple as lowering your standards and spending more money, then don't you think schools like Tennessee, Nebraska, West Virginia, Clemson, and probably 20 others I could name would be doing a lot more winning?