Elephant garlic is an odd little plant. It's more closely related to leeks than to garlic and has a tendency to alternate each year between forming one large bulb or 'round' and forming many small cloves.
Elephant garlic is a biennial and you get the single bulb in the years that the plants don't go to flower or seed. All of the plant's resources go into building up the single bulb that will help the plant survive into its 2nd year and set seed. If you re-plant the large bulb, you should get a plant that sends up a flower stalk and develops smaller cloves. When the cloves get large enough, they will repeat this cycle.
So you're doing everything right - it's just the nature of elephant garlic.