Banging my knuckles against something is never fun, and it's worse if it bleeds. The Mechanix or some other leather or textile glove can often keep the bleeding internal -- so hurt as it might, I won't have to worry about contaminating the wound as much and I can keep working.
After working on a greasy and gritty vehicle, the dirt can linger around for days. Oil generally washes off and most of the black crud can be removed with a green scrub pad, fine steel wool, or pumice but often some of it does stay around on small skin perforations or under nails. Some of us have to work in an offices with other people or meet with clients and such so cleanliness is a must -- especially if we have to shake hands. For some of us, we can do without the greasy hand experience.
I could drive to the car to the shop to get oil change or brake service, but where's the fun in that. I can have the experience while keeping somewhat clean...