Shit had to be rugged, and your standard uniform was not functionally all that different from some rougher everyday wear. My mother has a Swiss Army surplus coat from the 1950s (long before her time, even), still in fantastic condition, that she wears. You hear similar stories with other army surplus. It’s not until the mid-Cold War, when military clothing changes to camo and miscellaneous utility instead of “Stay warm, minimize logistic footprint”, that you start to get less of that quality of surplus.