Question

What could be a possible explanation why tectonic plates do not all move in the same direction?

Answer 1

If the plates squeeze closer at the boundary, they are moving in opposite directions. If they pull apart, they are moving in opposite directions.
If they are doing neither, then they are sliding past each other, in opposite directions.

Answer 2

volcanoc activities disturb the movement of the tectonic plates and this results in the changing of their direction and ocean waves also  play a major role in changing the direction of the tectonic plates so they move in different directions