I had no idea, I don’t really think of my family as having dark hair - but our hair is brown. Why are blonde hair follicles unaffected by laser treatment?
Edit: it seems like it’s less to do with them being unaffected and more to do with how the targeting system for the lasers work? That seems like something that could be improved one day.
Laser wavelengths targets melanin (a molecule with a specific color absorption and reflection), which is low in light colored hair or skin. Higher melanin density means a darker (appearing) color, so more opportunities for the light to react. This is why a dark hair color and light skin color has the best success with laser.