There are lots of reasons they aren't repairable. Lack of documentation and debug access is probably the biggest one. My washing machine died, and it looked like some components on the PCB blew. I bought a replacement for around £50 (already a crazy move) but sadly it didn't work. Not really anywhere you can go from there unless you're a professional washing machine repair man.

My fridge also had some kind of fault with the drainage tube (kept freezing up) but there's simply no way to access it. The back panel is not removable.

> PCBs that have been manufactured for decades ... same designs.

Absolutely not the case. Go and look up any washing machine control board. They're different for almost every model.

Washing machines & fridges may be better; I've never had to take one apart.

The only good solution to this problem I've come up with is requiring manufacturers to dispose of unwanted appliances for free. That way they have at least some incentive to make them last for a long time and be easily recyclable / repairable.