Why do computer techs have to charge you money to have them come fix your computer?

The same reason you have to pay a mechanic to fix your car, or a Doctor to cure your illness. A computer tech has a skill that you need to diagnose and repair your computer, Would you perform your job for free ?

Thanks to the internet there are lots of people that are around to help you help yourself though... Imagine performing that open heart surgery on yourself via the internet ;-P