>>20
The guy >>16 is writing code in his spare time and his employer owns the copyright to the code. So when he writes and publishes the GPL'd code, his employer is legally able to republish the code under any other license (as the copyright holder). By having someone else that is (probably) unrelated to >>16 and his employer, that someone else holds copyright to his own part of the project. This means that >>16's employer cannot trivially decide to republish the whole project under some other license. Now the code owned by >>16's employer is probably meaningless outside of the specific context of the GPL'd project. What this means is that should >>16's employer decide to republish the project under a different license, they would have to invest more resources to rework the project that they would control the whole project. It is a mere inconvenience that they don't control the whole project and they also want to republish the project under a different license. It is significantly easier for the employer to let it be: >>16 will continue to publish code to the GPL'd project and his employer won't try to republish the project under a different license.