With just a handful of creatures on the battlefield, Zada makes Expedite look like a better version of Ancestral Recall
The haste mode also ranges from a decent bonus to actively gamebreaking (i.e., with Jecht, Reluctant Guardian)
Also creatures are so powerful that tempo is of real importance in cube, both of which facts make equipment less powerful in cube
This connects several themes in MTG, like drawing two cards a turn, cycling matters, and graveyard-matters
You have to play some mostly-mediocre cards, you have to get them into your graveyard to start with, you have to replace a draw to get it back and mill yourself and there we have the crux of the problem
It has its own sacrifice archetype to slot into, but it's honestly just great in any black deck