Mains power switches are a wear item and can withstand like 10-100x less on/off cycles than a simple button that controls some 3.3V gpio on a microcontroller.
Or, if it's really 40 years old, "cheap" could be "really fat and expensive" today.
If you pick up an old "broken" power (audio) amp, the most likely reason for it to be broken is pots - switch - caps - FETs in that order.