The lithospheric plates move constantly due to the heat from the Earth’s interior causing convection currents in the underlying mantle. This movement is driven by the temperature differences within the Earth’s layers. Hot material from the mantle rises towards the surface, cools, and then sinks back down, creating a continuous cycle.
Additionally, the plates interact at their boundaries, where they can diverge, converge, or slide past one another. These interactions lead to various geological phenomena such as earthquakes, volcanic activity, and the formation of mountains. Essentially, the dynamic nature of the Earth’s interior is the primary reason behind the constant motion of lithospheric plates.