It's entirely a matter of climate. Here in the UK, there are, in any given year, no more than ten or so days on which one could be comfortably naked outdoors. Even then, it would only be in certain parts of the country (Devon, Cornwall, perhaps Somerset). Nobody in their right mind would ever go naked on the Yorkshire Dales, even on the hottest day of the year.

As a species whose evolutionary beginnings were in Equatorial Africa, our ancestors might have been 'naturally' naked, but by the time recognisably 'human' species such as ourselves, the Neranderthals and the Denisovans appeared, the family had spread ot parts of the world with very different climates. We all wore clothes, and, to an extent, the clothed state has become our ''natural' one. I also submit that the near-universal (even in the hottest climates) practice of covering the genitals has more to do with our unique bipedal posture. Everything is, so to speak, 'hanging out there', especially for males, and something which keeps it all from getting in the way, flopping about annoyingly, or being injured by thorns, etc is merely practical.