Not sure why all the park exclusives aren't sold at the Disney stores.
When the Droid Factory stuff was released, Disney went on record saying that certain Star Wars merchandise created for Disney Parks was primarily intended to offer experiences/shopping you can’t find anywhere outside Disney Parks. When you go there on vacation, they want you to find stuff in the Parks that you've never seen before - can't do that if all the stuff in the park is the same as the stuff in your local Disney Store.
Some stuff does eventually make it on-line or out to Disney Stores, but not everything will. Disney has said that most of the Galaxy Edge stuff will stay in that park for the experience for quite some time.
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