[flowerthoughts]

How did you conclude that they aren't the most reliable long-term?

Temperature sensing is extremely simple and cheap. Bi-metal contacts have been used since the dawn of electronics, and the solid state versions are also really simple. (Making components that are temperature invariant is the hard task.)

[gertlex]

Fair question! My speculation here comes from thermistors being relatively common replacement parts. (clothes dryers, ovens) As you mentioned, temperature-invariant is tricky, and I think it's often a non-linear but close-enough for the design. I have the impression a failure mode can be if the temperature-response behavior changes over time.

A bi-metal contact is only good for a single temperature, I think? (can be adjustable like thermostats) (I'm sure many but not all dish-washers probably do only need a single temperature...)