A wild guess would be that roughly 90% of all systems handling this are written in COBOL running on z/OS or IBM i. And that most of the developers are currently close to 60, spending their free time with their grandchildren and not on Hacker News.

I'm not much help either since I work with mortgages, and having it all explained during a lunch break might be a bit much. There are also, depending on company and country, rules and laws about what you can talk about.