Why? Honestly I have ZERO desire to see most people naked. Let's face it, most people's bodies are not very close to anyone's idea of perfection.
Have you looked around in the locker room at the gym lately? Yuck. We are all working towards a better looking body, but many have not achieved that ideal or anything close to it. This is especially true for older people who, even if thin, have various parts that sag or look bad. Clothes sort of decorate one's body, and partly hide anything ugly or flawed.
If our society evolved into one where everyone had to be naked at all times, I'd be out there with a protest sign marching and chanting "Clothes for all, now!"