In addition, that up and down motion is annoying to passengers, and a waste of energy. The suspension has dampers, and the tires have hysteresis (it takes more

In addition, that up and down motion is annoying to passengers, and a waste of energy. The suspension has dampers, and the tires have hysteresis (it takes more energy to squish a tire down than you get from letting it spring back up), so more energy is put into the "up" parts of the cycle than is recovered from the "down" parts.