no wonder barrel jacks were never used to transfer data…

Oh you sweet summer child. As someone who bridged the gap between analog and digital sensing systems, I assure you, they were. I think it would be hard for almost anyone who grew up/ technically developed in the all digital age to believe some of the wack-ass shit we used to do to make things work. I had a technical career in the military in the period of transition from basically hybrid analog/ digital systems, to mostly digital systems. There were PLENTY of systems that used something not any more complicated than a barrel jack for doing so. Power, communications, you name it. But these were very simple systems relative to what we do now. And the reason why matched your thinking throughout this post. They are incredibly robust, simple connectors. They can rotate without issue. They are incredibly common and can be widely versatile. They are basically bullet proof, and if need be, I could solder in a jumper or just pinch a couple wires together holding my fingers to make it work if the cable were to fail.

IIRC, and I’m long in the tooth so it might be a bit muddled, I remember it taking almost 2 days for one computer system to warm up (to quite literally warm up physically to temperature and become stable), and when we had to load the operating system, we used reel to reel digital audio tape. You quite literally had to manually move the tape back and forth to find the start byte sequence. And that system used a headphone jack to give you a digital output display (not entirely; the computer and display system for had to do the analog to digital conversion).