I was studying business in Australia when Aldi came in and had a tutor who was a little obsessed with them.
Most supermarkets (Coles, Woolworths/Safeway) employed a lot of cheap, casual or part time, high turnover staff. Award rates (Australia complicated alternative to minimum wages) are lower for younger employees (up to 21 yrs) so they employed a lot of high schoolers. The jobs were very narrow. Checkout chicks don't leave the counter. When no one is waiting, they need to pretend to be cleaning their workstations.
Aldi paid slightly above award. They preferred to hire adults. They preferred to hire for the long term. They had raises & advancement opportunities. They kept costs down by with efficiency instead of low wages. Intelligent efficiency with brains in use at all levels. Employees are far more independent. If there are long queues, they open another counter. If not, the stock shelve. If they have time, they take stock counts or do something else. The job satisfaction is way way higher.
The upshot of all this is that they can run stores with far fewer employees. A lot of other things go into this (store layouts, fewer product choices, display-in-bulk packaging), but better treated, more empowered employees is a big one. Hourly rates is just a part of the picture.