Tyranitar can learn Outrage, Gible can learn Outrage, they're both in the monster egg group, so why can Tyranitar pass on Thrash but not Outrage to Gible?
Is there a particular pattern to what moves can be inherited from which parent in Gen VI?
Most likely cause with the information provided: your Tyranitar levelled up enough to automatically forget Outrage in the Day Care, then you retrieved him (by accident?), causing his previous moves to be completely forgotten, then you stored him again, at which point he no longer had Outrage. If you want to make sure the move you're trying to breed down is not lost, do not retreive that Pokémon from the Day Care until you no longer need it.