To change settings, others also have a camera inside the fridge so you can see on screen the contents without opening it.

Why don't they make part of the door with that magical see-through material my windows are made of ?

Glass is not a good thermal insulator, and is more expensive than plastic.

My windows are insulated. Is it more expensive than a screen/camera/electronics ?

I see that a insulated (triple layer) window around 100 euros [ https://www.leroymerlin.fr/produits/bauplaza-fenetre-en-pvc-... ]. Let's assume this retailer makes a 2x margin, so real cost is 50 euro.

A webcam on Aliexpress is around 5 euros. Throw in a microcontroller that's like 2 euros on aliexpress, a 10 euro screen and you still have a 30-ish euro budget for the actual door that's probably plastic (acrylic and something like PE ?). So yeah, probably more expensive.

But that doesn't means that doesn't exists ! We can see that all the time in supermarket, but I guess their needs are different.

How did we manage to figure out a less convenient interface than a door and dial?

What do you mean? It was always inconvenient for the manufacturer. How do you show ads on a dial anyway?