Here's why:

* Wind as the Driver: Wind is the primary force that shapes and moves dunes.

* Sand Transport: Wind picks up sand grains and carries them along the ground. This process is called saltation.

* Dune Formation: As wind carries sand, it deposits the grains on the leeward (downwind) side of obstacles. Over time, this deposition creates a dune.

* Dune Movement: The wind continues to pick up sand from the windward (upwind) side of the dune and deposits it on the leeward side. This process causes the dune to slowly migrate in the direction of the prevailing wind.

Important Note: The exact direction of dune movement can be influenced by other factors, such as:

* Wind Strength and Direction: Changes in wind strength and direction can affect the rate and direction of dune movement.

* Vegetation: Plants can act as barriers, slowing or altering the movement of dunes.

* Topography: The shape of the surrounding landscape can influence wind patterns and dune migration.