As someone who has a garden and has successfully grown garlic from cut ends of store bulbs...
It's not worth the labor.
I garden, yes, but the economy of scales of buying at the grocery store is much lower than growing your own vegetables. You garden because you want to enjoy vegetables that are either heirloom or you want the freshness.
Between the labor, watering, fertilizing, maintaining, etc. it's simply cheaper to buy at the store.