...and this is why we need not only the full spectrum of licences from MIT to GPL but also organisations that watch over compliance... and sue if necessary...
The Software Freedom Conservancy and Software Freedom Law Centers are perhaps best known for copyleft enforcement, particularly regarding Busybox. They serve as copyright enforcers to well-known projects such as Git, GNOME, QEMU, Boost, Selenium, and Twisted.
The Free Software Foundation also does GPL Enforcement.