inertia
When a bird walks or hops it moves forward
maybe not in gear
forward and backwards
Inertia
forward friction on the tyres from the road..
A Lot!
What causes a car to move is gasoline.
Assuming the other seat adjustments work, and the switch tests okay, remove the seat, turn it over and inspect the forward/backward mechanism. You will probably find something broken.
The engine does. Sometimes the wind can be behind it too
to move said car forward ...unless using other form of power.........
The purpose of an accelerator is the car is to give the engine gas so the car will move.