Why don’t other planets and moons in our solar system show signs of plate tectonics?
Mars and Europa show signs of plate tectonics.
Plate tectonics requires a particular kind of interaction between a more solid outer crust - lithosphere - and a more fluid inner layer - asthenosphere.
Some geological features on Mars seem to indicate that it is undergoing or has undergone plate tectonics too according to UCLA professor of Earth and space sciences An Lin.
More recently, signs of plate tectonics have been seen on Europa.