Not a computer scientist, but surely COBOL could be machine translated to another more modern language - or even a dialect of a modern language specifically created to make such a translation verifiably correct?
My favorite example of this was a data entry routine that was insane - and lifted to a web interface circa 2004. “Turns out” when processing paper, several key transactions filtered through a gentleman, long since passed, who lost an arm in Korea. When paperwork was received, they were arranged and stapled in a way that accommodated his mobility limitations.
Every COBOL code base has stories like that, and there’s no functions or modern metaphors as it’s procedural. So your opportunities for code translation are really scoped to things that you can make a “black box”, never to be touched again.
Remember too this is shitty, unsexy, non-portable work. Top talent started looking elsewhere in the 90s, and often you’re left with a couple of people who understand how stuff works, then mostly folks who value stability over all else. Companies tend to pay for shiny skills, and the folks who really understand their business get second fiddle.
One perspective on COBOL and why it is such a "write only" language is that it's barely a stone's throw from an Assembly Language with a verbose BASIC-like phrasing. (Well, historically BASIC derives from lessons learned from COBOL rather than the other way around, but from a modern perspective you get the gist.) Every single line has the readability of English, sort of, with that BASIC-like face. Every single line has just about the simplicity of your average basic processor op-codes, just like assembly. To do anything reasonably complex you need lots of lines building up layers of complexity from the simple instructions, just like assembly. Trying to figure out the high level control flow and analyze the overall logic, just like in any disassembly effort, becomes a mind's eye puzzle because there's few ways to visualize the abstractions in the code because the code is at too low of a level for good abstractions. There's no functions and classes, just lots and lots of little instructions. Endless instructions.
If you translate it so that is does effectively the same, the resulting code is nice.
Unfortunately only the former can be automated. Also, you need to understand the code to do the latter. But reading it is hard and the ones who wrote it are dead/pensioned.