Also, sunk cost fallacy. Any reasonably complex COBOL application has lots of lines of code, which are easily counted and in some cases may have even been originally paid for per-line on expensive contracts still on file. That gives a lot of "weight" to that sunk cost on the books, even in timelines of half-centuries. "You want to rewrite a hundred thousand lines of once very expensive code?" you can hear the ghosts of bean counters past shouting in the corridors no matter how much you explain to them that they should have better amortized and depreciated those costs decades ago.