I think people would be shocked if they knew how much critical stuff operates on older technology.  Stuff that has been "modernized" still operates the same way.  A "modernized" system still "pushes a button" or "adjusts a knob" based on a reading that it "sees" from a "gauge".  In the case of the latest launch to space by SpaceX, those "knobs, switches, buttons and gauges" are still there.  The only difference is they aren't physical mechanical devices, they are "virtual" devices presented on a touch screen.

A concept of "hacking 101" is to look at how something works and understand it, then see what else it could do.  Can I make this gauge (physical or virtual) read a different value?  Can I make this knob (again physical or virtual) do something different other than it's intended purpose?

It doesn't take something having to be connected to the internet, stuxnet proved that.  All it takes is a little bit of "social engineering".  Drop a thumb drive in a parking lot with some malware and a few bogus pictures on it.  Somebody will find it, plug it into their computer just to "see what's on it" and you have a spread.

By the way, what stuxnet did was not just spin the centrifuges faster than rated.  It would do so then abruptly stop them and start them up again.  Imagine driving a car to 100 mph then slamming it into park, then repeating it.  Your transmission wouldn't last very long doing something like that.  That is exactly what stuxnet did.

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