Indeed, many who released source code under the GPL in the past did so with the conviction that the license itself would in some measure protect the source code itself — as source code — from being exploited by commercially entities.

The license was supposed to make derivative work feed back into improving the software itself, not to allow it to be used to create competing software.

Many of those are disappointed with leading free software / open source advocates such as Stallman for not taking a stance against the AI companies' practice.