For random software, yes, but in the case of UEFI firmware it's not really applicable, which is the context of the parent comment. You can go build a UEFI bootloader for the RPi4 from TianoCore right now. What you can't do is use the OS-level distro tools to package or "manage" that TianoCore-based UEFI firmware in any way.[1] You have to stick it on the device yourself, and that's not a coincidence: all modern UEFI platforms treat that boot firmware as separate from the host operating system environment, and they generally do not treat these updates as "package repository updates" in the typical way. That's why UEFI is an "interface", after all.

The correct way to manage that firmware, in the best case scenario, is to let the vendor produce a (correct) binary that is source-available, reproducible down to the last bit, and then use a system fwupd to apply updates that firmware in a generic way, like using UEFI capsules. Which is exactly the kind of project Tow-Boot is aiming to be: a base upon which vendors can create reproducible UEFI-compatible firmware.

Naturally there are exceptions to all of this (such as the infamous linux-firmware package which is managed by your OS packager) but I think you catch the drift. It's not a binary decision on whether to ship something in this way, it's a spectrum.

[1] What I mean by this is, you don't install firmware updates using apt or yum or whatever, like you did in the past with grub. You apply firmware updates using fwupd, which is a third party tool that actually integrates with UEFI to apply patches directly.