Probably two thirds of banking and insurance companies still use COBOL on the backend at some point because it's too hard to get regulators to approve replacements.

Is it a regulator issue? My impression was that it was just hard to switch from COBOL to something more modern. All the bugs and corner cases were fixed in COBOL, and now porting them to NewLang without breaking any of them is nearly impossible without a massive budget and undefined timeline.

Some COBOL programs are millions of lines constantly being updated by programmers to fix bugs and add features.

If you want to quickly learn COBOL: https://www.tutorialspoint.com/cobol/index.htm Try that tutorial. I learned COBOL in college around 1987.

Also the readability of COBOL code, audits are way easier.