I was told the reason for the mini fridge was the same reason why fans and heaters has timers on them. During WW2 and after, there was a shortage of electricity and being conservative with electricity was highly encouraged . And even now , people typically still follow that mindset.

It was also what encouraged the use of your water heating systems (we have water heater tanks that heat the water constantly but UK uses heaters that heat the water at use).

And I was told this is also why it's less common for people to have clothes dryers.

Well, full regular clothes dryers. I had a washer/dryer in my apartment but it was not like American ones.

Firstly it took like 3 hours to wash and "dry" a small load of clothes.

I was told it uses way less water than American washing machines.
It also did not have vents. And didn't really dry clothes.

It just spun out as much water as possible and applied a little heat.

All clothes still had to be hung out to dry.

Despite your claims that mini fridges are not common, the Internet says otherwise. Perhaps you just were lucky to have a full fridge.

https://www.reddit.com/r/AskUK/comments/qz7iii/how_do_you_survive_with_such_small_fridges/

https://wilshirerefrigeration.com/why-europeans-have-smaller-refrigerators/

https://www.reddit.com/r/AskUK/comments/qz7iii/how_do_you_survive_with_such_small_fridges/

https://www.reddit.com/r/Edinburgh/comments/10taeb3/why_do_almost_all_rental_flats_in_edinburgh_have/