Any idea why my vinegar never makes a mother?

I've been making barley vinegar every year for about 5 years. If I'm careful to aerate it every day or two for the first month or two, then it works well and ends up tasting much like apple cider vinegar. Some batches, I add a little Braggs live cider vinegar or the previous batch of barley vinegar as a starter, and sometimes I don't. The starter doesn't seem to make any difference, but failing to aerate it regularly for the first month or two does lead to moldy failure.

It has never made anything that seems a vinegar mother. It's not a problem since I'm happy with the resulting vinegar, but I'm curious if anyone can explain the vinegar formation process in way that helps me understand why this alcohol turns to vinegar but never produces a mother.

I start with 2 or 3 liters of local barley wine, called chang, which is made by an age-old process containing just barley and a local yeast. Chang is mildly alcoholic, not fizzy, nicely sour and sweet. I add starter or don't, keep it on a shelf in the kitchen, and every day or two, pour it into a steel pot and back into the glass jar. Most batches turn purple temporarily and then turn back to the original color. It gets a layer of yeasty yuck floating on top in the first month, so when that slows down I strain it out. It gets sludge in the bottom that looks like finely ground brown flour, and is hard to strain out, but eventually when new sludge stops being produced, I taste it and it is usually finished at that point. Then I pour it into nice bottles for the kitchen for salad dressing, or for gifts.  

I've never seen any gelatinous stuff floating or sinking in it at any point in the process. What gives? I'm at 10,600 feet altitude but I can't imagine that makes any difference.