Debian is (at least in theory) kernel agnostic, so it can't depend on udev, which is Linux specific.
You may never heard of /lib/udev/devices but that just means you never needed it. It was added when /dev started being a tmpfs filesystem (and now devtmpfs), because devices were no longer preserved across reboots.
At the time was not an API break, because people could still use a static /dev, and so was backward compatible. In the meantime other breakages occurred.
Anyway, the problem here is not this specific feature: it's the fact that udev AGAIN broke an API. The problem is not systemd or any other software, it's the fact people working on the core Linux plumbing are constantly annoying it's users.
This would not be a problem if we had some user-space wrapper abstracting this lower level stuff. But we do not, so please don't regard low level APIs as things that can change any time just because they can. They are as much standard APIs as brk(), sbrk() or malloc(), and there are people using it.