Fair use is an exception to copyright, but a license agreement can go far beyond copyright protections. There is no fair use exception to breach of contract.

I imagine a license agreement would only apply to using the software, not merely reading the code (which is what AI training claims to do under fair use).

As an analogy, you can’t enforce a “license” that anyone that opens your GitHub repo and looks at any .cpp file owes you $1,000,000.