Why do clouds usually form high in the air rather than near the earths surface

"High in the air" is a matter of opinion and perspective. And, clouds do form near the earth's surface, we just call it fog. Clouds are often seen hanging around the top of mountains as well. However, the reason clouds usually form up in the air is clouds are moisture, and the moisture evaporates and rises from the earth to where the air is cooler above the earth surface. The moisture in the air then condenses to from lots of little water droplets that form the clouds. Depending upon the time of year and how warm and mosit the air is and how high and how cold the cold air is depends upon how high and what kind of clouds form.