The middle of tectonic plates tend to have fewer mountains then locations near tectonic plate boundaries. What might be one possible explanation for this?

Plate boundaries will have more mountain ranges than the middle of the plates because the interaction of the plates at the boundaries are responsible for fold mountain formation.

Mountain ranges are formed at convergent boundaries where two tectonic plates (continent-continent and ocean to continent) move towards each other. As the plates crash into each other, powerful compressional forces fold the rocks upwards into mountain ranges.