There is no evidence of plate tectonics on Mercury.The MOST likely explanation is that:

Question

Quizplus · Accepted Answer

Plate tectonics require a certain degree of heat and mobility within the mantle to create movement and separation of the lithosphere. If a planet cools too rapidly, the mantle becomes too rigid and cannot create plate movement. This is believed to be the case with Mercury, resulting in the lack of evidence for plate tectonics.

There Is No Evidence of Plate Tectonics on Mercury