<Snipped quote by Caldizar>
Because it's not a limit to creative freedom—it's a solution to prevent a situation that gets arbitrarily more complex than it needs to be. I don't consider it limiting to say that there's an existing mechanic fits better than a fringe mechanic that isn't really used right now.
Except from my point of view Planes weren't a fringe mechanic until the World said they were a few posts back. I assumed, perhaps mistakenly, that it was actual lore that just wasn't heavily explored but still possible.
And yes, admittedly I pushed the idea even then, but that's because I'm passionate about it. Which is better I think, than me coming back in and dropping out a few weeks later due to a lack of interest.