The mechanical cameras have little question about their reliability and future fixability. Arguably the most capable of the 35mm cameras (ones that came out JUUUSSSTTT before digital) aren't the smartest buys, because people have gotten wise with all the familiarity with digital rot. When things become cost-prohibitive, manufacturers no longer produce replacements parts, and it's not worth it/unfeasible to do a low-count run of old circuitboards for things like obscure or amateur/semi pro cameras. Nikon FEs have a great user reputation, but people realize that once the circuitboards go (not talking about a simple re-soldering or that sort of low-level problem), they're effectively a paperweight. Nikon FMs of the same vintage are more expensive because they'll likely be able to be fixed by a skilled repairman.
Not that they aren't reliable or great buys, as they're dirt cheap. I'm just saying that in the long term, people have less faith in the early electronic cameras, and even up through the last ones, save for a few super-high-end ones like the F5/F6, which seem to be holding their value a bit better.
Similar thing with cars... Ones that are so old and basic they can be fixed with a wrench and some screwdrivers are a safe bet. Ones from the 70s and 80s that are plastic-fantastic and the first implementations of new tech like fuel-injection and other advancements are neither incredibly reliable nor easily/cost-effectively fixable when things go wrong with them.