If you don't abide by the terms of the GPL, you do not have permission to modify and redistribute code licensed under it. That means that their entire OS is stolen, and they are selling software they have zero rights to.
Allowing companies to get away with it fundamentally destroys the principles of open source code. Sharing literally every modification they distribute with literally zero restrictions that aren't part of the GPL isn't some nice to have. It's unconditionally mandatory to have any rights to touch the code at all.