Why would an EFI "BIOS" update break the EFI boot manager?

I had a similar problem after updating my BIOS and was asking myself why a complete restore of the hdd via dd would not leave me with a bootable system.

It seems that when installing the boot loader, the operating system must register an entry to the "EFI Boot Variables" inside the NVRAM. No entry, no boot. What makes this all the more confusing is that with UEFI specification 2.3 the system may look up a file EFI/boot/bootx64.efi similar to when booting from an external medium on the main hard disk, so some versions of UEFI might just boot up without fiddling around.

This registering should be done with efibootmgr but modprobe efivars fails for me as well, under ubuntu. So I also just chroot and reinstall grub-efi and hope for the best.