It’s GPL and they haven’t made contributors sign a CLA. So if anybody wants to relicense the Linux kernel, they need to get permission from every single copyright holder retroactively. This is infeasible.
CLAs exists to get this permission up front before any code makes it into the project, which is what enables projects like Redis to relicense.
BSD style licenses being more permissive than the GPL also contribute to this; you can incorporate BSD-licensed code into a new non-free version but you can’t do that with GPL-licensed code.
CLAs exists to get this permission up front before any code makes it into the project, which is what enables projects like Redis to relicense.
BSD style licenses being more permissive than the GPL also contribute to this; you can incorporate BSD-licensed code into a new non-free version but you can’t do that with GPL-licensed code.