Because we also supply the tile, cabinetry, countertops and hardware, closet finishes can be specified against what is already going into the room instead of guessed at from a separate catalog. If the vanity is white oak, the closet can be white oak. If the hardware is matte black, so are the pulls.
That is the practical argument for doing closets with the same supplier as the bathroom and kitchen: fewer finish mismatches, and one person to call when something is wrong.