I'll tell you why, because on my open top,, a rearward move of the hammer by only 1/8th inch allows the cylinder to freely rotate the tiny amount required to put it out of safety and onto a live cap.
I would never carry it on my hip all day that way. Getting in and out of vehicles, kneeling, standing, twisting bumping into things. Nooo thank you. 1/8 inch is too small a distance. Thong or no thong. My femur has a severe lead allergy, and I try to do everything I can to keep roundballs from entering it.
I'll use the safety notches at the range on the loading bench but thats about it.