I also took a COBOL class in college and the introduction programing exercise was pretty easy. However, this is like saying HTML is easy so anyone should be able to create a web portal.
As LostMyBeaver explained above, "The problem is that JCL, RPG, CICS, DB2 and all the surrounding infrastructure is very confusing." This would be the CSS, JSON, CGI, PHP, SSI, and other infrastructure that our imaginary web portal interacts with. Creating a static web page is fairly easy. Combining everything into a dynamic infrastructure takes time and multiple iterations.
Same with the COBOL code. The programmers experimented and found solutions to all the edge cases, all the system calls to the OS, all the file locking and transaction logging that is required for audits, all the database calls, etc. that would be difficult to transcode onto a different OS and hardware.
So finding replacement COBOL code might be something that AI can help with, but unless you build a virtual machine to replicate all the old system calls, then test your new code in C, Rust, Python, or the language of the day and then determine what OS and hardware you are targeting, you really don't have a replacement solution.
Transcoding old software is not the same as translating Latin into English.