GPL
Background
(Keep this short - 2 sentances.)
Sharing
The GPL is about sharing.
Commons
The GPL is a way to preserve a commons, while giving people the freedom to do what they want with the hardware and software. The GPL was invented when RMS when his colleague 'privatized', i.e. stole, a group project, emacs.
Dr. Adrian Bowyer and hundred of thousand of Linux user-developers find the GPL useful to prevent further rent-seeking theft by bad actors.
Further discussion may be beyond the scope of this webpage.