A mechanical volume control that actually works!

Like most everyone else, I have had many devices that included a mechanical rotary volume control. And as far as I can remember, on every single device, the volume control eventually failed, usually being the first problem. The symptom was always the same, eventually the low level volume would completely drop out, so that turning the volume up from zero would jump from zero to some low or medium volume level.

Ten or fifteen years ago, I bought a namebrand pair of computer speakers, 5 or 10 watts total. About five years ago, the main speaker of the pair, the one with the volume and other controls on it, began being used 24/7, with the volume adjusted regularly. Low and behold, the mechanical volume control still works flawlessly. I have used it probably 10 to 20 times more than any other volume control I have ever had.

Assuming my experience is common... Are decent mechanical volume controls expensive, or is it just that manufacturers go for the very cheapest volume control?

Yes, to both. The cheapest potentiometers (volume controls) are plated steel spring contacts onto carbon-paint resistive elements on phenolic plastic substrates. They work quite well, but the carbon is prone to oxidation and can be abraded; the plating on the spring can wear through or crack; the contact pressure can be uneven, and scrape through the 'paint'. If contact pressure is too high, it wears through the conductor. If it's too low, the contact may be impaired by any bit of dust or dirt.

High-end controls use low-pressure-high-contact-area wipers (extra parts here), on non-oxidizing conductive films with high strength, sometimes there's a sandwich of conductors with the top layer being a lubricant/ contact enhancer ('conductive plastic' is typical). Really high-end controls use no moving parts at all, the knob is just an input to a digital controller that programs a variable-gain amplifier or multiplier.