It's not totally clear why Samsung is ending the rewards scheme. Perhaps it was just so successful in getting people to use Bixby that it wasn't necessary anymore, but probably not. A more likely scenario is that people were finding ways to game the system, rack up a ton of Samsung Pay points and use those to grab a bunch of gift cards. Though Samsung is ending the program, you still have a few more weeks to grab those points, and you'll still be able to use the background colors you've unlocked after My Bixby Level shuts down.