Hover bikes are still susceptible to the laws of gravity, therefore also to impacts from drops. Since they require normal force to keep itself above the surface, resisting the gravitational force, there is an unseen form of surface that they traverse on. Also, with such a drop, the sudden change in velocity will also apply force on the bike, therefore it is also there to absorb the force. A plane flies, but if it suddenly drops in altitude, the passengers will feel a sudden force applied on their body. The shocks are definitely necessary if you understand physics.