> "Model weights are not source code, but data."

OK but I mean it's functionally a kind of machine code for a strange machine with a neural transformer architecture, like a 'binary blob'. It's outside of the paradigm where machine code is created only by compilation of copyrightable source code written by humans following their creative "aha moment".

They are only protectable by copyright you the degree they are creative works of authorship. Copyright is not usually how these are protected.

Copyright protection is what gives protection when you put something out into the public. The desire to not publish something is evidence against having these protections, because people know they are not copyright able, so for that reason and others they keep it private. You just presented evidence against your position.