Tech debt is can come from risk adversity or from taking risks on new shiny things. I think you're right that as long as technology is a moving target, it's always going to be there. To me, the trick is not cornering yourself in a situation where your whole ecosystem is essentially abandoned and not rewriting for the sake of chasing the latest craze. That means parallel re-development, from scratch, of all the existing features, on something like a 10- or 15-year cycle. You want to pick a technology you're certain won't sunset in the next 15 years (with upgrades and further development along the way, of course), then spend a couple years rewriting everything in parallel while still running your old system, test it in every way possible, then blue/green it. I've done this three times in my life for one company on the same piece of large business software.

Companies should think of their software the way automakers or aircraft manufacturers think of their platforms. Once new feature requests are piling up that are just more and more awkward to bolt onto the old system, you have another department that's already been designing a whole new frame and platform for the next decade. Constantly rolling at a steady pace prevents panic. Where this breaks down is where you get things like the 737 MAX.