@Background Pony #7A6E
 
Nah, makes sense to me. They’re going with a “The shadowbolts aren’t bad, really!” angle, based on the dance magic song and the general theme they seem to be going with.  
So the dazzles are going to learn about friendship and make a heel face turn at the end, with Indigo zap being pretty good.
 
Lightning dust on the other hand they probably want to keep as a unsympathetic “bad” character, so she wouldn’t fit in this scenario as they feel lightning dust isn’t really a good character.  
Plus, the shadowbolts all mirror the mane six’s elements (like sugar coat being honest), where LD isn’t loyal at all.

@Dr Outback
 
Because no one cares about the dolls, it seems.
 
I wish her animated design resembled the toy more — rest in peace red streaks and longer hair.

People are still bothered about Indigo Zap not being Lightning Dust but no one talks about how the movie version of Indigo Zap looks really different from the toy version.

@Background Pony #7A6E
 
Some random issue in production, I think.  
Leaked images of the prototype dolls showed what seemed to be Lighting Dust (same color scheme). But then no, it’s Indigo Zap.
 
However, there really is no confirmation if Lighting was ever meant to be in the movie (that would be a good thing to ask after the movie premieres), or even if the doll was Lighting Dust in the first place (coincidences, even the most unlikely ones, do happen).

Even her eye color is the same.
 
Only reason I can figure they didn’t use Lightning is that these girls are hiding something.

Yeah, yeah.. what about that ear accessory and the hair and changed skin?

Can you try?

XD

An editing program and tons of free time says otherwise.