Clouds are moving fast because they are being carried by wind, which tends to blow faster at higher altitudes in the atmosphere. The speed at which clouds move depends on the speed of the wind at the altitude where the cloud is located. Higher in the sky, winds are generally stronger, so clouds appear to move faster. This explains why sometimes clouds seem to race across the sky at great speeds. Factors affecting cloud movement include the direction and strength of the wind, solar heating causing air movement, and terrain like mountains that can force air upward and shift cloud positions. The average cloud can move anywhere from 30 to 120 miles per hour depending on these factors.
In short, the clouds are moving fast simply because of strong winds at higher altitudes carrying the water vapor droplets that form clouds.
