One reason might be that this only existed in Paper, which is a downstream fork of Spigot, which is (sort of) a downstream fork of CraftBukkit, which is a set of patches to the official minecraft server.

Another reason might be that this only does anything if there are many players on the server, and you hit a region loaded by someone else. Might be difficult to think of that. You'd never come across it if testing in singleplayer.

But in essence I agree, it's surprising that no one else found and reported this years ago!