I’m not an expert either, but I’m thinking of what happens when you aren’t careful about those coily phone cords. They can intertwine onto themselves quite easily, much more easily than straight cords. I imagine it has something to do with the coils nesting into one another.
A “s” shaped stand of hair will nest into another “s” shaped strand. This complex with then come together with another complex, which then joins another. Eventually, depending on how curly the hair is as well as its length, no more hair can be added to the super-complex, and then you’re left with a ringlet.
Super curly hair will not form ringlets naturally. I know this from experience. I have wavy hair on the sides of my head, and cute little ringlets will sprout out in these areas. But the back of my hair is more tightly curled, and does not “ringlet” up. My hypothesis is that the curl is too tight to permit good “wave formation” back there. Just think of the hair back there being “z” shaped. The hair strands does not join up into simodal complexes and super complexes, choosing instead to rejoice in frizzy clumps. The hair in the back of my head is bushy; to get curls I must put in rollers at night.
However, locking is best acheived with hair that is less likely to “ringlet” up–that is, tightly curly hair (aka “kinky” hair). “Z” shaped hair is more likely to bunch up into tangles than “s” shaped hair, which comes together in smooth waves. Wearers of big afros know this: if they aren’t careful about picking out the fro frequently, tangles form–breaking the smooth roundness found in good-looking afros.