It's not just to reduce the amount of ZoL specific work.
If I understand correctly, the developers were saying there are specific parts of Linux where anything using them is considered a derivative work, and therefore even distributing source would be a violation of GPL. An instance of this is the crypto layer that was added in recently with the native dataset encryption. SPL actually reimplements this logic because the ZoL maintainers claim they can't use the Linux crypto subsystem without violating GPL.
If I understand correctly, the developers were saying there are specific parts of Linux where anything using them is considered a derivative work, and therefore even distributing source would be a violation of GPL. An instance of this is the crypto layer that was added in recently with the native dataset encryption. SPL actually reimplements this logic because the ZoL maintainers claim they can't use the Linux crypto subsystem without violating GPL.