Why do smaller dunes usually move faster than larger dunes?

Smaller sand dunes generally move faster than larger ones because of their physical dimensions and the volume of material involved in their migration.

A dune moves forward as a whole when it reaches a state of equilibrium, where sand is eroded from the windward side and deposited on the leeward slip face. Because a smaller dune has a smaller cross section, it requires less total sand to be transported by the wind to reconstitute its form one dune-length downwind. Conversely, larger dunes possess a greater volume of sand, necessitating a significantly higher amount of material movement to achieve the same degree of displacement.1