Why minelaying submarines still carried torpedoes

Did World War I minelaying submarines have torpedo tubes?

Yes, usually, but some carried only the torpedo loaded in the tube and no reloads because mines were their main weapon.

The details varied substantially with submarine size, from the small UC I type to much larger boats. Many carried one or more torpedo tubes, but the smallest examples might carry no reloads at all: the weapon already in the tube was their entire torpedo armament. Their primary offensive load remained mines.