This can happen if a tire is badly unbalanced (or not properly dynamically balanced), or from a combination of a slight unbalance and bad shocks, or from an extreme misalignment. In rare cases, there may also be a mismatch of a particular tire design (usually only at a narrow pressure range) and the designed harmonics of the car's suspension. All of the above should result in vibrations easily perceptible to the driver long before the cupping is visible, and I can not imagine how any of them could happen to all four tires at once -- two at one end, perhaps, in rare cases, but not all four -- usually only one at a time. This is a real puzzle, unless the tires were a defective batch, like those notorious Firestones on Ford SUVs; I suppose that if someone with a pre-ABS car locked up all four brakes in a long skid and flat-spotted all four tires, and then didn't have them skimmed and rebalanced right away, it might cause all four to be cupped eventually.