A friend of mine worked for a logistic company and he told me many times that dealing with Aldi was a nightmare for them because they were extremely demanding:

very thin profit margin, tough quality checks (when delivering the items to the warehouses the checks were done on many more samples and in a much more detailed way than what other supermarket chains did) and if the truck arrived at the warehouse anytime after the agreed delivery time you were basically screwed (ranging from at least having to provide a discount to the whole delivery being rejected therefore having to find another chain willing to buy it or just throw it away).

All this might as well explain (additionally to your "shelf life") the good & cheap onions.

I'm an onion lover - Go onions! :)

(ps: this is just a neutral comment - so far I mostly ignored Aldi, excluding the exercise bike I bought from them which is still working perfectly ~3 years later)