Twinkle Eyes are kind of not Twinkle Eyes unless they have...well...twinkle eyes. That is the entire point of the set so if they're willing to revise Sparkler's hair because it's not close enough to the original (speculated reason), it would be odd for them to produce this set without the key feature of the set. Would be like selling the Rainbow ponies with different hair.
Not that I rule it out, it just seems pointless to issue this set without issuing the key feature of that set.
Then what's the point of making them at all? They can't be Twinkle Eyes without the rhinestones.
It's fair that if they are going to advertise them as the Twinkle Eyed set that it makes sense to include that feature.
My thought process is just that the jewel eyes might be integral as a unifying feature to the set but not integral to the character design?
I don't know that the Rainbow ponies is the best comparison. If you took the Rainbow feature away, you would then have to redesign part of the pony. To me, the twinkle eyes are more like glitter symbols or flocking. Plenty of people would have bought the previous Basic Fun ponies if they had painted symbols only. And plenty of people currently collect non-flocked and de-flocked versions of So-Soft ponies.
And also, plenty of people collect Fizzy merch when the art depicts her with regular eyes.
Although I guess they could put glitter on their eyes or something? But I would guess they'd give them jewel eyes. Unless they couldn't figure out how to keep them securely in place. (Like, to make sure they aren't a choking hazard.)
I mean, that's a legitimate possibility. Additionally, lots of non-pony people find the jewel eyes creepy. Depending on how much they are banking on pure nostalgia* or how much they want to draw in a modern audience that just likes the idea of a classic MLP with little regard to how authentic it is.
*True, they changed Sparkler's hair which seems to indicate that they are listening closely to collectors. On the other hand, Sparkler's hair was an easy fix where as the twinkle eye gimmick isn't something that could be changed mid-stream.
I have NEVER seen a pony with an eye popped out unless it was on purpose by a customizer. Just rock (ho ho like a GEM) solid.