Exactly. Safety-critical applications by nature have to be risk-averse, and that means anything new, anything that hasn't been thoroughly tested and backed by years of experience, is an unacceptable risk.
Older processors constructed on older large-size processes and often operating at higher voltages and slower clocks are more robust because they have a smaller number of transistors, which means a simpler more predictable model of error propagation; larger features mean lower current densities, increasing resistance to electromigration and decreasing the chances of defects from natural process variation; higher supply voltages reduce the effects of noise; slower clock rates allow more time for noise-induced glitches to settle instead of propagating.
One of my favourite examples of this is the CDP1802 - an 8-bit CPU from the mid 70s, which is still in production and use today in aerospace applications.
Older processors constructed on older large-size processes and often operating at higher voltages and slower clocks are more robust because they have a smaller number of transistors, which means a simpler more predictable model of error propagation; larger features mean lower current densities, increasing resistance to electromigration and decreasing the chances of defects from natural process variation; higher supply voltages reduce the effects of noise; slower clock rates allow more time for noise-induced glitches to settle instead of propagating.
One of my favourite examples of this is the CDP1802 - an 8-bit CPU from the mid 70s, which is still in production and use today in aerospace applications.