I like to think that someone (probably in the Adult Timeline as I suspect that might be easier to discover the split from albeit the Child Timeline is another prospect, I personally don't believe the Fallen Timeline could be it because I subscribe to a theory from a YT vid by VortexxyGaming that the Fallen Timeline was actually the original where Zelda never got any visions and so never helped Link, then Zelda the First used the combined Triforce after AoL to send the dreams back to the OoT Zelda to change history) learned about how the Timeline got split and tried using the Triforce to unify the Timelines, but didn't realize there were three, or at least the consequences of such a merge attempt, and somehow that merger more or less set up the events of BotW. Granted, this is a complete layperson theory as I have yet to play BotW, but yeah that's my thought at least for now.