You can't hack a system you can't access.
So very true. As part of my university's CS program, a course that covered fundamentals of operating systems was a requirement. I hope the class still covers the Principle of Least Privilege and what happens when systems/users don't abide by it. The TL;DR is that neither everyone nor every process needs to run as an administrator/superuser and this can cut down on a good number security issues and stupid stuff like an end user either inadvertently or intentionally trying to do nefarious things within the OS environment such as a lowly end user trying to access another such user's files or attempting to execute the command to reformat the master network disk drive.
Hand in hand with this is
@Ghostse's comment. The fact that companies believe that every device ranging from refrigerators to automobiles -- and everything in between -- should be internet-connected is alarming. In these devices, security is an afterthought and that assumes it's even being thought about to begin with. I still remember the evening news having a clip where our auto reporter showed how easy it was to hack an automobile and get access to critical systems such as the brakes through either the internet access provided for entertainment purposes or the bluetooth used for system diagnostics. Applying the principle of least privilege, only those objects that have a legitimate need to connect to internet at large should be allowed to do... with sufficient security to minimize the opportunities for unauthorized access.
This is why those older "antiquated" systems are still in use. Access is severely restricted and there tend to be safeguards in place to make sure those systems don't connect to the outside world.
Someone such as Brianna who thinks these critical systems simply need to be upgraded with a typical Windows OS also overlooks the fact that hackers tend to target the latest (usually Windows) operating systems because modern-day code isn't sufficiently tested and secured, making it easy to compromise. Look at all the Windows updates and Flash patches that get released
ad nauseum because of some buffer overflow or other critical bug that's been discovered and needs to be patched ASAP before hackers exploit them too badly. It's better to stay with what's hard-tested and proven to remain stable and/or reliable. Above all, KISS... keep it simple, stupid.
The problem with security through obscurity/obsolesence is that it's extremely difficult to source replacement components that are no longer being manufactured.
This is true, but so long as the hardware remains functional and is properly maintained (and hopefully not something new enough to have planned or forced obsolescence incorporated into it), why shouldn't real-time, mission-critical code be run in the same stable environment for as long as possible -- provided that proper security protocols are in place and nothing unnecessarily connects to the outside world?
I would laugh my ass of when it finally is elected and then becomes a member of a committee like the House Subcommittee on Livestock and Foreign Agriculture.
Why inflict Brianna's bullshit on a superior life form

?
[E: Added missing words]