Why is there less moisture in the air at high altitudes?

As everyone knows, moisture is also present in the air, because water from the surface of the earth simply evaporates and enters the air. Now let’s figure out if the same amount of moisture is everywhere. The thing is that the higher you go, the colder it gets, this is a natural process, but besides the drop in temperature, the moisture indicator also falls. There is a certain level at which they are, especially those from which rain falls and above which they do not rise, hence the air above them is much less humid.