I think at least part of the answer to this question is that there is a long tradition of wearing long nails in East Asian and South East Asian countries. Consequently, working with nails is a skill that almost everyone acquires to some degree in those countries. I had a professor who was born in China, and when he got his first teaching job, he brought his father over from China to live with him in New York. The first thing the father did was to grow his nails long, to show that he was now a gentleman who didn't have to work with his hands.