Banks remain with COBOL because they have a fuckton of COBOL code and 4 people can write it. There's nothing more to it.
Now, 4 million people can write it.
Now, 4 million people can write it.
A model being able to ingest the whole codebase (maybe even its VCS history!) and take you through it is almost certainly the most valuable part of all.
Not to mention the inevitable "now one-shot port that bad boy to rust" discussion.
One year from zero to senior doesn't sound that hard, does it? Try that with a Java codebase.