If the issue is more specifically copyright infringement, then leverage the legal apparatus in place for that. Their lawyers might listen better.
This is not a strongly held opinion and if you disagree I would love to hear your constructive thoughts!
The best way to make sure your code isn’t copied is not to publish it.
It basically happens like this:
"Oh this code solves our problems and has a nice community around it for network effects!"
**developers proceed to adopt codebase without checking the license**
**months later**
"Oh, huh this license has some interesting language in it..."
Then the employee doesn't mention it; because the risk of having to re-do a bunch of work feels higher than the risk of getting in trouble for violating a license. Basically, unless it's Oracle; people just kinda shrug it off as a "wontfix".
My whole thing is that any system depending on people to read and follow a license is quite flawed in terms of enforcement, and is largely designed specifically so that powerful encumbents can make claims, not individual developers.
Laws have to be enforced or people will ignore them. If there's no practical way to enforce a law that doesn't involve violating freedoms - you're kinda fucked.