The breakage of ZoL wasn't a side-effect of some big technical change. They literally just made the SIMD enable/disable barriers no longer usable from non-GPL modules (the changed an EXPORT_SYMBOL to EXPORT_SYMBOL_GPL). This means you can't use SIMD-accelerated hashing functions from ZoL -- and there is no way to fix it without hurting performance other than reverting the "license change". And the entire justification for this change was "there are no in-kernel users".
Now, they are obviously free to do that and ZoL needs to work around it. But it's silly to argue that this was not an intentional breakage of a system which many people use and cannot be worked around out-of-kernel. Yes, it's not userspace code but it did cause regressions for users. Linus and GregKH have always disliked ZFS because they feel it was designed to be incompatible with Linux (and they're entitled to that view, however wrong it may be) so it's unsurprising that they are against doing anything that may help ZoL.
Now, they are obviously free to do that and ZoL needs to work around it. But it's silly to argue that this was not an intentional breakage of a system which many people use and cannot be worked around out-of-kernel. Yes, it's not userspace code but it did cause regressions for users. Linus and GregKH have always disliked ZFS because they feel it was designed to be incompatible with Linux (and they're entitled to that view, however wrong it may be) so it's unsurprising that they are against doing anything that may help ZoL.