Comment # 1 on bug 1173023 from Takashi Iwai

This is the designed behavior.  kernel-default is present only for serving to
the older kernel that doesn't support the compressed firmware loading, hence
unless you have the old kernel, kernel-firmwware-all is preferred.

You made a choice to keep the old kernel-firmware, but then you must tell
zypper (via addlock).  Otherwise zypper cannot know whether it's still an old
system to be updated.