I figured it was a trademark issue. Didn't Hasbro lose a lot of the rights to older gen characters for basically neglecting to reapply for them? Walmart might have been trying to save on royalty
The shirt has Applejack on it, which is one of the trademarks that Hasbro held onto, so that's not likely. I honestly think they just ran some focus groups with girls ages 5-40 and found a bunch of people that liked the older gen ponies and only had passing familiarity with the term "bronies."