I know how you feel, it seems as if they just choose random aesthetically pleasing ponies without putting much thought. As long as they can appeal to mainstream people who barely know anything about the franchise and don't care about specific G1 ponies, and just buy the merch because it feels trendy and retro. This probably only says poorly about my own knowledge, but when G1 retro merch started popping up, I didn't even know Starshine's name (Back then I mostly knew the names of ponies who appeared in the cartoons, and the original six).
Even so, they don't have to use her again and again and if mainstream people really don't care about what ponies are on the shirts they wear, there are lots of other aesthetically pleasing ponies that would have the added bonus of appealing to fans.
But even with the other characters they do choose, they mess up the colors a lot.
For example, on the tag of these flip-flops, why is Tootsie colored like Firefly?
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Then there is this dress. It may be hard to discern because of the small image, but some of the ponies aren't recognizable to me. Like who is that purple unicorn with Lickety Split's cutie mark? And the unicorn colored like G3 Cotton Candy... And, this time Tootsie is in Medley's colors.
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