Why do weather changes only occur in the troposphere?

The troposphere is the layer of Earth’s atmosphere close to the ground. It is also the densest layer in the Earth's atmosphere. It contains about 75% of the mass of the entire atmosphere and almost all water vapor and aerosols.

Due to the large influence of the surface, the horizontal distribution of meteorological elements (temperature, humidity, etc.) is uneven. The regular vertical movement of air and the irregular turbulent mixing are both quite intense. Water vapor, dust, and heat are exchanged and mixed in the upper and lower layers. Since more than 90% of water vapor is concentrated in the troposphere, many weather phenomena such as clouds, fog, rain, and snow occur in the troposphere.