For six mana you get 9/9 worth of stats, and when you encore it you not only get to swing a 6/6 at everyone, you get an instant army of nine tokens which stick around
Either you want a card you want to build around - one who does something you want to do, and therefore want to support in the deck with synergies - or you just think theyre powerful and like the colours they give you
Steel represents powerful characters who can hit hard, defend staunchly, and bring home tons of Lore, while Sapphire represents tactics and careful planning
Most newer players wouldn't know either one, but I have to imagine there would be a ton of love from longtime players to see new versions of any of these
However, the return of the Eldrazi titans Emrakul, Ulamog and Kozilek does imply some continuation from the Zendikar storylines