Why most aircraft flying below tropopause layer and why supersonic plane fly at stratosphere?

In a Propellor driven aircraft, the propellor winds it's way through the air in the same way as a Ship propellor winds through the water. If there is not much air, then the propellor has nothing to pull through and it spins fast but does not move forward very fast. At high altitude there is not much air so the plane has to fly at much lower level where there is plenty of air. Jet aircraft use the fuel to push very hard against the turbine blades and the exploding fuel thrusts against the turbine blades, and forces the plane forward as the burnt fuel leaves the plane. With jet aircraft the thin, sparse air at high altitude is not such a problem but it still needs air to cause fuel combustion. Jet planes can fly at higher altitudes. With space Rockets that power off into space where there is no air, they achieve combustion by using chemicals that contain oxygen, and the thrust of the burning fuel leaving the rocket, pushes against the rocket, and moves it forward into space toward the moon or where ever.