> Linux is GPL and I doubt it would have tens of thousands of authors if it were not.

Why? There's plenty of permissive F/OSS projects with large numbers of contributors.

> It would have a dozen proprietary forks.

Probably, but proprietary forks don't stop F/OSS contributions. They can even be the source of them, as upstreaming everything that isn't secret sauce reduced the cost of maintaining the proprietary fork. A number of the big sources of F/OSS contributions to Postgres are maintainers of proprietary downstream distributions (I don't know that all are strictly forks, since I think the proprietary bits of at least some are using the extension mechanism.)

> Why? There's plenty of permissive F/OSS projects with large numbers of contributors.

Companies invest in developing Linux to create a commodity they can leverage to sell their products and services. The GPL ensures the investment remains a commodity and cannot be used in proprietary products that can't be also leveraged by the initial contributor.

There was a lot of BSD in the core of every proprietary Unix, each tied to a given manufacturer.

> There was a lot of BSD in the core of every proprietary Unix, each tied to a given manufacturer

Except MacOS X, the major proprietary Unixes all predated permissively-licensed releases of BSD, and the early permissively licensed releases were under a copyright cloud for years that prevented anyone from relying on them for commercial downstream distributions.

The GPL doesn't have this advertising clause - it's largely specific to some BSD variants.

That's why Linux doesn't come with a 10,000+ page tome listing names ;-)

> "Linux is GPL and I doubt it would have tens of thousands of authors if it were not."

Aren't the BSDs a counterexample to that?

How many authors they have? My impression is that the number is much lower.