it probably isn't.
as having them switched makes more sense. I never understood why the y axis was the vertical one.
seems sensible to me as the y axis goes up in a two dimensional grid, why not in the third dimension?
but i understand that when you make a 3D grid you apply the 2D grid to the surface of the world, making both the X and Y lateral, and making the Z going up via process of elimination
it all depends on preferences i guess.