Because it would totally suck.
No one wants to be the victim of theft, but being a scam victim will certainly leave you feeling particularly humiliated. That's why you ought to pay attention to this lovely thing that's been happening. Thieves in several US cities are targeting people at gas stations as they fill up their cars. The scam works like this: The thief pulls in first then goes to the pump. However, he/she doesn't use their own nozzle. Instead they take one from the other side and put it in their gas tank. Then they just stand and wait for their victim.
An unsuspecting driver will pull up and grab what they assume to be their nozzle, but not before sliding their credit card into the machine. Then they start pumping gas not into their car, but the thieves'. One only realizes they've been ripped off when they get back in the car and start it up to see the gas tank still empty.