VPN is used for telecommuting. Without VPN, the company would have to expose a lot of intranet services to the internet for us to be able to work from home, and to be on call at night would entail staying at the office all night.
The fact that the first (only) use for VPN you can think of is to hide criminal activity says a lot about you, really.
Because it can protect the sensitive (internal corporate network) information while its travelling over untrusted networks, with the destination being none the wiser.
Bridging two networks (or a host and a network) together securely over the internet has far more applications than merely telecommuting and is so effective and easy to apply, why not use it to protect your Facebook session while you're at the coffee shop?
The fact that the first (only) use for VPN you can think of is to hide criminal activity says a lot about you, really.