Reasons: it's hot, job, easy to clean, I do it every summer, tradition, 'murica!
It's also how I protest the obsession of fashion and appearance the the American people seem to love dropping gagillions of $$$ into. Kind of like we need to focus on other things besides ourselves all the time. I'm in South Lake Tahoe (rich town) and it's like a parade of people being excessive... JMHO