I won’t speak for all “white dudes” but I know why I do it.
First, my thermostat is just different from average. If it’s 70F/21C, there’s a very high chance I’m going to be sweating, especially if I’m indoors and there’s limited air movement or I’m outdoors and there’s any bit of direct sunlight. Shorts make that a bit more bearable.
Second, given my warm nature, the climate where I live and my lifestyle make wearing shorts practical for much of the year. In the “colder” months of the year, it’s usually a case where it’s cold in the morning but warms up to a reasonable extent during the day. Guess what? I have an indoor, office job. I don’t give a flip about how cold it is during the early parts of the day because I’m going to be indoors where the temperature is pretty much guaranteed to be above the 70F/21C limit I mentioned in my first point. By the time I’m off work and out of the office in the evening, it’s warmed up to the point where shorts are totally appropriate and comfy (for me). Sure, I could waste time and energy doing multiple wardrobe changes throughout the day, but that’s just bullshit and quite frankly, stupid, if I don’t have to do it.
Third, who gives a fuck? Apparently a lot of people – as it’s very common to get questions or comments when I wear shorts during colder weather that lesser humans can’t tolerate in shorts. I don’t go around acting as the fashion police for your stupid crocs or question your multiple changes of clothes per day like you’re Beyoncé doing a concert. So leave my cargo shorts in the middle of winter alone.
I’m heavy and my calves are like rocks from supporting all this mass. Those bastards are working their ass off when I’m walking they’re often dripping with sweat. If it’s over ~5c it will look like I slogged through a shallow stream - my pants will be visually wet within no time at all.
I was diagnosed with leukemia a couple years ago and a funny moment during treatment was my toes getting cold for the first time relative to my body temperature. I’d never experienced that before - it blew my mind and I became such a baby about it. It was totally intolerable. I finally understood what all the women in my life complain about regarding cold feet. … Who knew?

