Humans have been making music for tens of thousands of years. Singing bonds people together, exercises a range of muscles and makes you feel happy.
The camaraderie of communal singing is of benefit to people - have you noticed how much everyone enjoys singing en masse at football matches and religious gatherings with no thought of their own ability? You don't get that feeling when listening to a CD.
Singing is good for your health, it lifts the spirits and you can do it for free (if you're really lucky, people will actually pay you to do it!) - so what are you waiting for? There's so much you can do...