Comment by Analemma_

As much as everyone likes to poke fun at COBOL, the language itself really isn't the problem with maintaining/updating old COBOL systems. It's old, but it's not that bad.

The real problem is the entire ecosystem around those systems. Remember, a lot of COBOL software dates back to a time before things like relational databases. You'll be working with flat files that might, if you're very lucky, have column and record separators and useful names/documentation explaining what they are. If you're unlucky you'll have to figure out field widths from the code and infer what the fields are based on their actual usage. Oh and if you get it wrong you just messed up something related to payroll or financial compliance; enjoy the punishing fines.

That kind of stuff, more than the language, is the reason nobody wants to touch old COBOL systems.