This is anecdotal and might not be super useful, but it kinda backs up what GrouchySquash8923 is saying.

I used to bite my nails to the extreme, constantly bleeding on the sides of each finger.

I had pretty tough days in my life and undiagnosed ADHD.

Once things got more comfortable I pretty much stopped biting my nails constantly and only did it when they needed trimming.

Then I got my ADHD diagnosis and now I only bite if they are so long that they bother me AND I can't find a nail clipper.

So might be a combination of things. Thanks for coming to my TED Talk.