They don't have public transportation or live in large cities where they have to worry about those type of things.......durr.Fyi most mammals do have clothes it's called fur.
Animals do live in large cities as pets and owners do bring them on public transportation. Fur is not an entrapment like clothes are. Fur is natural, animals are born with it. Fur also does not prevent bodily fluids from coming into contact with surfaces outside of the body.
About your disease point:
The way I see it, so what if someone has a disease, let them spread it and let people die from it. [There's too many people on this planet as of now anyways.] Not everyone will die from it. People who survive a disease have genes that can be passed on to future generations that allow them to survive such diseases. It would make the gene pool stronger. It is part of evolution and natural selection- survival of the fittest.
Our society of medicine is making a weaker and weaker gene pool as time goes on. People have to rely on medicine more and more to keep them from dying from disease. One day it will explode in our faces as our genes become so weak and people become so fragile, and they can't survive any sort of illness on their own.
And a possible solution to the disease on public transportation from no clothing (which is a highly unlikely scenario anyways) would be to have some sort of small and cheap disposable towel or sheet or something that people could sit on if they need to ride public transportation. Or people with certain diagnosed diseases could be not allowed to ride public transportation unless they wear some form of cover up. Just suggestions, not saying they are the best ideas, but they are ideas. I know there could be some simple solution to said "problem." We can send men to the moon, so I'm sure we could figure that one out.
Why so worried about disease anyways? A girl with a STD on her vagina could scratch her vagina and then touch doorknobs and then you could touch that doorknob and touch your balls and get the STD she had. Or other types of diseases too, not just STD's.