There's a very specific part of the brain responsible for the movement planning and fine motor control required for writing. Some folks have it underdeveloped, and need to spend an inordinate amount of effort and concentration in order to write. And even then, their writing will often degrade over time as they fatigue.
I first head about Dysgraphia 10 right here though - the symptoms a familiar enough for a self-diagnosis, but as all self-diagnosis there might be something else.
Although in grad school I never used to a digital method of annotating papers and did it by hand anyway.
If a student has a medical condition that makes it so their handwriting is not legible then they probably had the same issue in HS and should be able to navigate College bureaucracy well enough to get the exemption status.
Not to be too personal, 99% of college students (including myself back in the day) are lazy rationalizers in some fashion. In my experience it's not until Junior/Senior year that some majors start squeezing that out.
Most people do grow up tho.