Question

why does temperature decrease with height

Answer 1

As the pressure decreases, air molecules spread out further and the temperature decreases. If the humidity is at 100 percent the temperature decreases more slowly with height.

Answer 2

$\huge \underline \mathfrak \pink{ANSWER} \over$

Temperatures decrease with increasing height because the atmosphere distributes itself according to gravity. Pressure generally decreases with height because the pressure is determined by the mass of the atmosphere above some point.