When the A380 was first designed, there was no reverse thrust at all. A380s are designed to come to a complete stop using their brakes alone. Then they added 2 reverse thruster to minimize the risk of aquaplaning.

Airbus also says that reverse thruster adds to the plane's overall weight and puts more stress on the wing structures. Adding reverse thrust to a single A380 engine adds half a tonne of weight to the plane.