The owner of a copyright or trademark or Name/Image/Likeness is legally allowed to monopolize its intellectual property for a very long time. It's not a violation of monopoly laws for entities such as MLB and the MLBPA to license a single business entity (Topps or Fanatics) to produce and market items that bear the likeness of players and the logos of teams. It's perfectly legal if that's how those entities want to do business. It's also legal for them to license multiple entities (think back to Topps, Fleer, Donruss, etc.)
On the other hand, it is not legal for Topps or another card producer to attempt to control or monopolize the market of a certain type of sports cards if another card producer also holds a license from the sports teams and players' association to produce cards.
Subtle, but important differences.
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