It's apparently a common thing: Kids who are "smart" and are clearly naturally interested in learning, are not followed up usefully. They can read novels and some basic multiplication, but have to sit in school and say the alphabet out loud and add single digits for months. Before proceeding to be told to read basic sentences for another few weeks, etc.
They are not pushed and challenged like their classmates. The teachers think everything is FINE because they are not behind, but the kids spend a full decade not learning to study properly because they don't ever have to. They rather learn that they can fuck around and wing it and it will be passable.
Then at some point, age 15 and up, they are getting to proper challenging stuff. Armed with zero habits, no experience in failing, no experience in planning and organizing and studying methodically... Many drop out, burn out, get depressed, or all of those at once.
I am in this picture. I excelled in school almost all years and graduated in the top ten of my high school class. Then I went to an engineering school and got my ass handed to me. I managed to graduate after 5 years, but it was a struggle and my GPA was noticeably worse than high school.