Why the negativity?
If someone wants to have fun in COBOL, let them have fun in COBOL.
If it’s agentic fun, that’s cool. If it’s an interest in the language, that’s cool. It’s not like you have to have an ROI for a fun side project.
It’s also OK to be turned off by AI use in hobby projects and it is also OK to prefer disclosure of the use of AI in projects so I can make that choice.