Yes, they are identical, except the name.
As in some cases, you’d need to be able to control how specific projects either import or export symbols.
Note how it says: “for this library”.
I’m not saying the situation cannot be improved. I just answered your question: why are these files copied?
(we could consider creating another layer of macros that only takes a name and then specialises a template, another possibility could be to use CMake’s GenerateExportHeader module (but there may be requirements/constraints that made this impossible/undesirable for the ROS2 codebase))