alt Hacker NewsWe have no data on how much has not been contributed back due to corporations forking code or just copy pasting it into other projects. For all you know permissive licenses have dramatically reduced contributions back.
We only know when they contribute, we have no data on when they don't. Stories like LLVM are good evidence for what you are saying, but the linux kernel is good evidence against it. Dozens of companies are forced to work together for the common good at a scale and level of resources that is unprecedented. Without the GPL this simply wouldn't (actually from an economic / game theory standpoint it couldn't) happen.
It's true that we don't have any definitive data on this.
But I buy the article's argument that upstreaming a patch once is simply cheaper than maintaining your own proprietary fork forever. It externalizes the efforts of maintaining it in the future. This means that public, community-maintained, permissively-licenced projects are a good deal for companies, and should win from the economic / game theory POV