With flying and ward on top, Tivit is a tricky commander to block , so you could be taking people out of the game through combat damage in all those extra turns you stack up
In Standard, even non-typal decks play Cavern of Souls often naming Phyrexian just to make their Atraxa, Grand Unifier uncounterable
Thank you for reading, and stay hot
I think it was to do with how the two cards performed in standard relative to each other
That being said, if your opponent doesn't have access to many chump blockers Su-Chi Cave Guard becomes a must-remove threat that will provide you with a ridiculous amount of mana whenever your opponent kills it
Fatal Push and Drown in the Loch are a great split of interaction, with Drown in the Loch in particular literally just being a Counterspell/Terminate split card