It gives green decks in Commander a way to nab their key lands, like Gaeas Cradle, without dedicating a full card slot to doing so
Only this outcome would cause the rules committee to ban the card
2017-02-09 While you're casting your free spell, the Expertise spell is still on the stack
The effect extends to their adversary, meaning it can be used to derail their strategy
Its also just a generically good card in casual Commander, so theres demand there too
While there aren't many obvious Legacy or Vintage staples, there are a ton of cards that will be heavily played in Commander and some new legends that, while not quite on the level of Atraxa, Praetors' Voice, will be the foundation of a lot of Commander decks