That’s because the COBOL OGs are retired/ing and the industry has been training young people telling them “yeah, sorry, this is all we can pay you”. Here in Europe, they’ll take unemployed people from a different industry, put them on a training course, and bang! you’ve got a grateful new dev who doesn’t know how much they are worth.
You just gotta keep spreading the message. I keep happily sharing my salary, especially with younger, less experienced devs, so we can all win better.