Covering garlic with 3-4 inches of straw over winter is recommended, so that probably doesn't account for your single clove harvest.

We don't know why the bulbs failed to form cloves.  The plants might have been harvested a little too early, or some vagary of growing conditions might have caused the single corms to develop.

Although we can't vouch for its validity, the following information from Gourmet Garlic Gardens may be of interest:

"As garlic goes through the development underground from a clove to a fully cloved bulb, it first swells into a large round undivided ball with a lot of wrappers that are almost fused together. As it grows, it begins to divide and sub-divide into as many cloves as it can before the heat causes it to lose its leaves. If the temperature increases before the garlic has time to divide, then the result is a large undivided round. Every time we harvest we find some of them. If replanted as is in the fall, they will form large fully divided bulbs the following spring. These rounds have the same taste and other properties as the clove they came from. Mild tasting garlics yield mild tasting rounds and strong garlics result in strong tasting rounds. For spring planting, rounds are your best bet to produce a good size bulb by the time early summer heat forces maturity."

Go here for basic garlic growing information from the University of Minnesota:
https://www.extension.umn.edu/garden/fruit-vegetable/growing-garlic-in-minnesota/