The software version of driving a car until it falls apart instead of doing more than the bare minimum to keep it running. It's not always the wrong choice but it's wrong to be surprised when faced with the expected outcome.
Add to that list "and there is basically one guy still qualified to work on the system", which is practically the case now for old COBOL banking systems. See http://cobolcowboys.com/
Businesses think once it's written it will always just work...and that's true if the underlying OS and hardware never change, and the business never changes, and requirements never change. But even if it's a completely niche application whose requirements never change, after a while the hardware breaks, and we can't buy the same, and we can't license the old OS or it has documented problems that won't be fixed, so we have to use a new one, and we can't get the old software dependencies to work on the new one, etc etc.