This is a much deeper question than you think. I have to go out for a bit but if this thread is still live when I come back I’ll give you a comprehensive answer.
In brief- it’s a cultural beauty standard created and enforced by women for women.
Why is nail art considered beautiful? I mean it’s art, it’s beautiful colours, sparkly and shiny sheen that fun and makes us feel feminine and expensive. Hyper femininity is a hallmark of black female fashion.
The impracticality of the nails is secondary in our minds becuse as black women we are used to impracticality when in comes to our bodies and grooming.
Everything from hair, dress, skin care, and hygine is multifaceted and layered. It requires work and effort because we have been told since the day we were born that our natural selves, hair in particular, is not enough.
This is the mentality we have around beauty so the nails being in the way of basic functionality is no sweat off our backs because we’re used to working living our lives this way.
Essentially it’s: hyper feminine beauty/culture norms + acceptance of impracticality.
I hope that kind of makes sense to you.