In 1993, after Alpha/Beta, Wizards of the Coast decided to put out it’s first expansion. Based on the book 1,001 Arabian Nights, the Middle-Eastern themed Arabian Nights expansion was planned for a December release.
This being early on in MTG’s card making, there was a lot that wasn’t set in stone. That included the iconic brown back and blue lettering card backs. For Arabian Nights they planned something, well, different. Namely this:
Instead of brown and blue, Arabian Nights would gone gone purple and gold to help make its mark. A problem, however, soon arose as game designer and playtester Skaff Elias noticed that, with a mix of original and expansion, the other player could easily tell what the other player had in their deck from the get-go. Even a cursory look before a match could have your deck made. And thanks to this being before the era of card sleeves, this would have been super hard to avoid.
Needing SOME way for designers to differentiate expansions, the expansion symbol was placed to the side of the front of the card so decks could be anonymous again. However, the changes were made so late that lands were not all removed from Arabian Nights, so only one land, a lonely Mountain, was printed in the expansion.
Despite the near miss, the choice to swap a different back with a symbol has not only stayed around for over a quarter of a century, every other card game followed it. Plus, Wizard’s of the Coast wouldn’t have to waste time working up new color combinations for the back.
In the end, by keeping a singular card back Magic gave itself a familiar face and a later iconic look that helped cement its place as the foremost card game in the world.