Imagine yourself writing a javascript library to do some mundane thing then releasing it as GPL and then somebody made a slightly modified copy of it and licenses it to google for 5M a year.
The generally held opinion on this is that that would never work, because Google has no reason to pay 5M a year to something that is available to anyone for free. The keyword is "slightly modified" here which implies that the modification is trivial. If the modifications are not trivial, then all bets are off of course.
