Well, it makes it really easy to get people to post which branch the page they're on is part of when they're making a bug report...and other than that, why does it matter what branch any random player thinks they're on at any given time?
Well, what matters to the player is what branch his character is, not what branch whatever game mechanic is using.
Devs: "New looting mechanics for testing"
Player: "Oh, this is stable, so I don't need to take it into account"
Player suffers effect of new looting mechanics, is frustrated by the surprise
Bug reports and other such things sometimes encounter similar issues with confusion about what continent is stable and isn't.
It's certainly not a huge deal. But it doesn't seem useful to anyone but the devs to distinguish which pages are testing and which are stable, so might as well hide the info?