My main reason the added wind protection on colder days and the protection against gettin my legs wet during rain or when the brush is all wet.
Yes shotguns are warmer., But I don't always need a lot more warmth.
Try wearing chinks, vest, bandana and cowboy hat around any of the national parks. I frequently tell my wife that there are more photos of me sitting on european coffee tables than she has at home. The tourist can't seem to take enough photos of western cowboy.
Just staying warm
Some guys just like to look the part
I've seen chinks that are slip on, Where there are no fastners. The leather is sewn to fit your thigh. I've seen them, with zipper and mine has 3 straps that buckle. And I agree, I want the buckle to be on the outside of my thigh where I don't sit on it.