Stability and reliability are primary goals of sensible flight related computing. That's why NASA's Space Shuttle used computers and software long frozen
in decades past. The old stuff was indisputably stable and reliable.

What I have always heard (note: I am not saying this is the actual reason) was that when you use 'old' computers, those computers are less prone to bit-
flipping by radiation from space. Even though such systems are generally built pretty fault tolerant (an odd number of units performing the same task with a
voter behind it, for example) the older chips were fast enough and simply a bit less prone to the bit-flipping.