That decision was made by the frame builder. Whether it's designed for full length housing, or only a bare wire depends on the size of the hole and possibly what's inside the tube.

For full length housing frames have an elongated oval hole, so the housing can enter without making a sharp bend. Some have a tube running all the way through and brazed or bonded at both ends.

For bare wire, the holes will be stepped and function as cable stops, with a base hole small enough that only the wire fits through. These are the ones that are the hardest to work with, but usually not easily converted to full housing through routing.