Question

Why does all weather phenomena take place in the troposphere?

Answer 1

Basically because that is the layer where most of the water vapor exists, as well as it is the layer where the greatest energy imbalance between the surface and the atmosphere exists. As a result nature tries to restore energy balance in that layer by various means, such as convection, and the effects of those processes we call weather. And hence all the weather phenomena take place in the troposphere.