Due to the intense competition in Germany, companies such as ALDI and Lidl are far more efficient than grocery stores in other countries, particularly the UK and US. Walmart tried to enter the German market years ago and was sent packing shortly after. The reason why the German stores are expanding is because there is very little profit to be made in Germany, whereas in other countries margins are much higher in supermarkets.

Also all three (Lidl/Schwarz Gruppe, Aldi Nord, Aldi Süd) are private companies and somewhat obfuscated. No shareholders demanding high dividend yield or quarterly forecasts. They operate in secrecy, even when the ALDI founders died, the most recent photos available to the public of both were made 30 years ago.

Small stores, mostly own labels and fewer employees. They buy only packages that don't need unpacking, saving a lot of time getting products on the shelf. Employees work all positions in the store so that shelves are filled when it's less busy and everyone is at the checkout when needed. That way no employee is idle, saving salaries.

In the UK they also profit from their European footprint. If you go somewhere else in Europe, you'll find that most products (nearly everything except for some food items) are the same as in the UK. They can buy in much bigger amounts than even Sainsbury's or Tesco as they operate in most European countries.

They also have barcodes on just about every side of the packaging. The cashiers don't have to figure out which side is the one with the barcode, they can just slide it across the scanner in whichever orientation it's on the belt. This makes checkout super efficient.

They also have very speedy checkouts, where the bagging is done by the customer at another table. This means one employee and checkout lane can do the work of three.

Also, I've heard they pay their staff the most out of UK grocery stores.

UK: I wonder about Waitrose and how WF was like it. Waitrose is owned and run as a cooperative, which I imagine is both unique and less easy for Amazon to buy.

This is only possible because they make their own products too. If you are Coke and need to compete with Pepsi you need to use the surface of your product to help with branding. If you are the only game in town you can have a white can covered in bar codes that says beer on the side.