Share the Spoils Text

Why doesn't Share the Spoils say "Once during each player's turn, that player may cast a spell or play a land"? Every person I have shown the card to in person or online did not know it was a once per turn until I saw it on the rulings page on Gatherer, and I feel just adding that small bit would make it clear.

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My best guess is there wasn’t room in the text box to add extra rules text.