Good Point! This combination among other does indeed take you back to the starting point. This idea is worth investigating.
However, the purpose of this practice is to only eliminate unnecessary moves being in opposite direction to avoid redundency in the path sequence/.

Because opposite directions aren't side by side. Do you end up in the same place? Yes (if the path is plain), but to eliminate them they should be side by side, or after some elimination, become as such, that's a requirement.

Can someone explain to me why the path ["NORTH", "WEST", "SOUTH", "EAST"] is not reducible even though you end up at the same place? That seems to be the point of this kata