The problem isn't around knowledge, but that it requires equipment not expected to be in a normal home. A house can have tools available to fix large mechanical objects, but not extremely delicate electronics that require an electron scanning microscope to properly fix.
Best thread summary of the year (OK, so the year is still young...)
Seriously though, most houses will have a toolbox with sufficient "stuff" to at least make a stab at fixing mechanical parts (Hammer, screwdriver, awl, pliers). For electrical items, a bit more "stuff" is needed (soldering iron, multimeter), but still there are enough people interested that it can in the house.
Electronics, now is basically "when it breaks, it's trash" (although there are groups of people who are dedicated to restoring 1990s vintage computers - probably the last generation where a steady hand with a soldering iron could still work, and the motherboards weren't multi-layer)