“The Commonwealth Bank of Australia tried to rewrite a core system in a fresh language; the project cost twice as much as they expected, $1 billion in Australian dollars. Len Santalucia, the longtime mainframe expert, once worked with the financial institution DTCC to investigate the possibility of converting their COBOL to Java.
“They probably have about seventy-five million lines of COBOL code,” he tells me, “and they found out that it would cost them so much that it would take, maybe, a couple of lifetimes to recover. It was ridiculous. And they have more money than God.”
So the banks shrug, and figure, screw it. If it ain’t broke, don’t fix it. Keep the old COBOL running”
https://www.wealthsimple.com/en-ca/magazine/cobol-controls-your-money