Comment by hakfoo

There's also 4) Manufacturers could position the price of spares at a level that's intended to provide pressure to scrap salvagable devices and put the customer back into the market. The classic "it will be $150 to send the guy out, and the magic PCB is $250, while an entire new washer is $550, are you sure you want to throw money into an N-years-old unit? (Bear in mind this calculus applies to the people who are not even considering DIY repair)

5) Manufacturers are burdened with selling the entire spares catalog, while third parties may concentrate on the highest-turnover items that they can sell easily.

Years ago, I looked at the service manual for a 1980s stereo receiver, and the manufacturer literally starred the parts they mentioned as most commonly needed for replacements. (The part I needed was, unsurprisingly, on that list)

I wish we'd see more in the way of "open PCB" appliances. 90% of "white goods" appliances (washers/driers/dishwashers/fridges/stoves/microwaves) have a board somewhere that reads a membrane keypad and a few sense switches and activates some relays and displays a timer. You could probably design a master PCB that replaced hundreds of different models, with different cable harnesses and firmware configurations for each model.

This would dramatically reduce the number of SKUs to stock, but at the cost of the master PCB probably costing a few dollars more because they can't strip out every non-essential component for lower-end models.