Here's why:

* Plate Boundaries: The Earth's crust is divided into large, moving plates. Where these plates interact at their boundaries, immense forces are generated. These forces cause the crust to deform in various ways.

* Convergent Boundaries: Plates colliding create compressional forces that lead to mountain building (orogeny), folding, and faulting.

* Divergent Boundaries: Plates moving apart create tensional forces that result in rifting, volcanic activity, and the creation of new oceanic crust.

* Transform Boundaries: Plates sliding past each other generate shear forces that cause strike-slip faulting.

Other factors that can contribute to crustal deformation, but are secondary to plate tectonics, include:

* Isostasy: The balance between the weight of the crust and the buoyancy of the underlying mantle.

* Volcanic activity: Magma intrusion and eruptions can cause localized deformation.

* Erosion and sedimentation: The removal and deposition of material can alter the stress distribution and lead to deformation.

While these secondary factors can play a role, plate tectonics is the dominant driver of crustal deformation on a global scale.