A big reason for struggling in college is that college is simply a poor fit for many kids.
Similar to how some girls are forced into engineering because there aren’t “enough” female engineers, college is often seen as the only path to success and happiness, so many kids are sidetracked by starting college (and not doing well) before finding their place in the world.
My experience is that kids with high GPA’s + rigor do the best in college. But forcing this model on everyone would be a disservice to many.