Here's why:

* The troposphere is the lowest layer of the atmosphere. It's where we live, and it's where most of the air's mass is concentrated.

* It contains the majority of the atmosphere's water vapor. This is crucial for cloud formation, precipitation, and other weather phenomena.

* Temperature decreases with altitude in the troposphere. This creates instability, leading to air currents and weather patterns.

* The tropopause, the boundary between the troposphere and the stratosphere, acts like a lid. It prevents most of the weather from reaching higher layers.

While the troposphere is the main stage for weather, some atmospheric phenomena, like the aurora borealis, occur in higher layers like the thermosphere. However, the day-to-day weather we experience is primarily a product of the troposphere.