This is due to the Sun's differential rotation. The Sun doesn't rotate like a solid sphere. The equator rotates faster than the poles. This means that sunspots at the equator will appear to move faster than those at higher latitudes, creating the westward motion.

Here's a more detailed explanation:

* Differential Rotation: The Sun's equator rotates once every 25 days, while the poles take about 36 days.

* Sunspot Movement: As sunspots are embedded in the Sun's plasma, they are carried along by this rotation. Because the equator rotates faster, sunspots appear to drift westward.

* Apparent Motion: This westward movement is actually an illusion caused by the difference in rotational speeds.

It's important to note that sunspots also move with the Sun's overall rotation, which is from east to west when viewed from Earth.