By your argumentation, it doesn't seem that this is a decision the
author of the library (or kernel, or whatever) gets to make, but
rather something which is inherent in what's been created; they can
offer their own opinion on what constitutes an application's use of
the library being "intimate" enough to create a derived work, but
have no special authority on the subject.
In other words, nothing binding would change if they were to
s/EXPORT_SYMBOL/EXPORT_SYMBOL_GPL/. They simply don't have any
say in whether my use of their work is a derivative work or not,
and these "EXPORT_SYMBOL_GPL" seem like documentation that says
"we believe use of these symbols probably means you're creating
a derivative work"--the derivative-work-ness is not actually a
result of these tags (and the tags might be wrong).