My oldest was a solid C student in high school who got some Ds and Fs too. He struggled with organization and learning disabilities. A 4 year college was not for him.
He’s at a tech school with smaller class sizes with great professors who want their students to succeed. He’s able to take 4-5 classes at a time versus the six or seven he had to take in high school. Just having less classes to juggle has really helped him a lot. The other huge factor is that he feels like he’s taking courses that he is interested in or that truly matter to his degree which has greatly improved his motivation as well.
I think you can get straight A’s in high school but if you enter into college without really knowing what you want to do or not having any true connection with your classes I can see how it would be easy to fail. Or if the child has zero financial investment in college themselves I can see them not putting much effort either as it’s no skin off their back. going to a smaller school has helped my son because he feels like the professors truly know who he is so if he does not show up in class the teachers will notice so that holds him a bit more accountable