Question

why do the lithospheric plates move

Answer 1

The lithospheric plates moves because of the movement of molten magma inside the earth.

Answer 2

As the interior of earth contains magma,it results to move the crust...therefore since the formation of earth,the lithospheric plates have been moving...and due to this,all our continents will merge into one continent called "pangea ultima"after a few millon years....

hope it helps,
thanx