Why though?

On top of that, there's the widely held assumption that the memory chips that back EFI variables in this industry, as well as the write mechanism is the firmware to write them are not of the highest quality. Because of that people generally try to minimize writing to them. Hence, it's best to keep regular writes out of nvram space, and rather do them in the HDD instead. Hence, registering new kernels always in efi vars is things most people involved try to avoid, and focus instead of leaving NVRAM as static as possible and instead just update the HDD instead.

Hence, altogether, I think outside of very specific setups (which I think VMs probably qualify as) I doubt you want to use solely UEFI BootXYZ variables as poor mans boot menu.

(people typically have other problems with it too, i.e. that the boot menu UI configured that way is not reachable the same way in the various firmware implementations – if they have an UI for that at all)