This ability has the potential to close out a game before your opponent even gets to draw a card under the right circumstances, so in order to avoid this scenario, they preemptively banned the card before it became too reliable.
If you have this card, you can search for Link, Hero of Time
Theres also the inherent benefit of deck-thinning, though from a statistical standpoint its not exactly clear that deck-thinning is all that fruitful in a game of Commander
Buy any 10 and get 40% off
Then, those cards must be combined to make a new library, and players must draw new hands
Depending on the creature type you pick you might have a few lingering creatures on the battlefield, popular creature types like Elves and Humans will likely see a few hanging around, but the spell should be more than enough to empty the board