> GPL is not necessarily for developers to get productive work done.
Try getting some productive work done without the source. Like fixing a printer of a proprietary driver, for instance. No, the GPL is about exactly about getting practical work done. That's why it emphasizes so much on the 4 essential freedoms, and why 3 of those 4 freedoms are essentially the same thing "the freedom to tinker with the source code and share that information with other developers who can tinker with it some more and do the same".
There is nothing preventing those users to publish that exact thing for the world to see. The GPL ensures that they can absolutely do that, so your point is moot.
The restrictions of the GPL only kick in when you distribute your binaries. You have the freedom to run and modify the source as you wish. The only rule is, "The source code travels with the binaries" - meaning /if/ you choose to distribute it, and you may choose who you distribute it to, that those who receive the binaries must also receive the source code and can take full advantage of the GPL just as you have.