The maintainers likely don't own the copyright on the entire codebase, and so likely cannot license it under anything other than the GPL. Incorporating GPL code

The maintainers likely don't own the copyright on the entire codebase, and so likely cannot license it under anything other than the GPL. Incorporating GPL code into an app on the app store is not possible without breaking either the app store's rules or the GPL's rules (most likely the GPL, which would effectively remove the maintainer's rights to distribute that code).