There are two parts to grub. The piece that lives in the EFI and the piece that lives in userspace.
When you update grub and/or call grub-mkconfig that updates only the userspace components.
When you call grub-install, it updates the part in the EFI. The issue here is that new functionality was added and you need an updated grub in the EFI for it to be properly supported. Historically this has not been the case.