Because handshaking has been around forever and old habits are hard to break. I stopped years ago after getting the "bone-crusher". People pick their noses, and their teeth, and some even still sneeze into their hands and you know they didn't run off to the bathroom right after to wash them. I posted about a dental hygienist doing EXACTLY that right in front of me. Then she thought she was going to work on my mouth? Our "interaction" brought the dentist running to see what the problem wash. smh
Speaking of which... not everyone washes their hands after using the bathroom. But back to handshaking being around forever...
Archaeological ruins and ancient texts show that handshaking was practiced in ancient Greece (where it was called dexiosis) as early as the 5th century BC.
en.wikipedia.org
Americans have been shaking hands with each other at least since the 17th century, when Quakers, who explicitly denounced exhibits of social hierarchy, used this as their form of greeting and taking leave. That said, clasping hands has not always seemed to be a great idea in the United States.
Trace the history of the handshake from Babylonia and the early Greeks to the present.
www.pbs.org
It's a habit I'd love to see go to the wayside, but I don't see it changing. No way to get billions of people to all decide it needs to stop, unfortunately.