Why are climatic regions distinguished within one belt?

In each climatic zone, it is customary to distinguish several climatic zones. There are several reasons for this. The relief has a very great influence on the formation of the climate. Indeed, on the plain, the climate is slightly different from the mountain one, and therefore the relief and height above sea level become very important factors in the formation of the climate of a particular region. And another important factor is the distance from the seas and oceans, because sea air and continental air have very different effects on the weather and climate in one or another part of the continent.