It happens, but very rarely. Everyone develops occasional PVC's. It is not something to be overly concerned about. In the average person, with occassional PVC's the chances of cardiac arrest are about the same as you being struck by lightening.
It's not that simple of a comparison. There are dozens of reasons for PVCs.
It's sort of like asking why haven't they cured cancer yet, or wishing for the cure. There are hundreds of different types of cancers and they call react differently to chemicals (medicines).
There are people with PVCs who are at higher risk but it's not because of the PVCs per se, it's due to the root cause which could be something like ARVD, or a defect, and having these issues creates symptoms like PVCs.
Don't focus on the PVCs themselves. Focus on the health of the cardiac muscle. Knowing the health of the muscle is a much better predictor of future mortality than just knowing PVCs.
That said, for people who have documented PVCs with a structurally normal heart muscle, their future all-cause mortality is the same as the general population. That means they have the same chances of death risk as anyone else.