The full year might be nicer, but personally I like this idea - it immediately let's you know how old of a version (or its initial feature set, in the case of LTS) you have installed.
For example, in the case of Ubuntu or Unity (the engine) you can tell what you're looking at, at a glance.
For Ubuntu people often use the codename (including in quite a few UIs, like [1]), something it presumably inherited from Debian, which does the same. I really dislike it, because I usually know which version number I want, but I rarely know which codename I want and always have to look it up on Wikipedia or the like.
[1]: https://packages.ubuntu.com/search?suite=kinetic&searchon=na...
Not only do they all start with the same letter, but the initial sound is nearly the same, too. It's way too easy to confuse them.
The nice thing of being at the start of a millennium is that after version 99 you can just move to 100!
I guess it's nice to have code names, but you still need some sort of a reference to remember what is what and it's the same kind of extra step that you'd have to do with version 1.2.3. Years somehow feel more memorable, at least to me?
Though I've also run into issues with package management. For example, I want to setup a repository that has packages for Ubuntu 20.04 (focal), but I'm using say Linux Mint 20.3 (una) which is based on it locally, because that might be easier to use as a desktop OS (no snaps) or something like it.
Some packages out there have instructions to setup their own repositories to get up to date versions, like Docker does: https://docs.docker.com/engine/install/ubuntu/
echo \
"deb [arch="$(dpkg --print-architecture)" signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
"$(. /etc/os-release && echo "$VERSION_CODENAME")" stable" | \
sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
deb [arch=amd64 signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu una stable
deb [arch=amd64 signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu focal stable
But at the same time, it's interesting just how much stuff the code names are used for and how things can break. I don't really have a solution, unless we want to have codenames be hierarchical, like bullseye_focal_una to indicate everything - the Debian, Ubuntu and Mint version in the example, and then have more intelligent tools pick the closest thing that exists.