I think part of it has to do with a tipping point: if you can hire up a good chunk of the key contributors and run with it, then it's easy to make a proprietary

I think part of it has to do with a tipping point: if you can hire up a good chunk of the key contributors and run with it, then it's easy to make a proprietary fork, and at the same time weaken the open source project. The GPL prevents this. No, it doesn't. Those key contributors are still the copyright holders of the code they contributed, and they are free to redistribute those contributions under different terms. If they all work for one company, they can just license copies of their code to that new company under non-GPL terms. The GPL fork still exists, but now a new, closed-source version of the code can be made with all of that (now-)employee-written code. If there are enough of those components, that company can just rewrite the code contributed by others that were only licensed under GPL, and now they have a mostly duplicate version of the same program, able to be extended and resold without source code. Digium does this for the Asterisk project. They have a GPL version that everyone is free to use, but nobody else is allowed to redistribute it without the source code. However, they make all contributors to the GPL project license their code to Digium so that Digium more-or-less owns the code, which Digium then turns around and sells under a closed-source license to companies that don't want to give their changes back to Asterisk. https://www.asterisk.org/doxygen/trunk/Licensing.html https://www.asterisk.org/doxygen/trunk/Licensing.html https://issues.asterisk.org/view_license_agreement.php https://issues.asterisk.org/view_license_agreement.php