I think its more so they're both too scared to ask each other to a nice event and since the prom is a highschool event, technically they wouldn't have to ask each other to go together so people are leaning towards it
Plus I think people have a really romanticised version of proms/ dances in their heads compared to like an important work event that could change your life energy
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Sorry about the gigantic post(/TДT)/ It's not about the prom itself. It's the communication. The prom is just the setting.
Koga's world is expanding now. She is showing herself more, is talking more to people, she's more confident and finding opportunities to get into music. That should be good. But even though it's good, Aya is feeling left out and lonely, and at the same time she has found out she really really likes Koga. Now, you have a prom, which people consider to be special, or a romantic event. Aya wants to go, she wants to be there with Koga, but they can't because of the recording company situation.
So how can Aya properly talk to Koga about how she's feeling, considering that her feelings are quite egoistic, or might make Koga feel uncomfortable about their friendship? She doesn't feel she can. So she's taking the sidelines and giving space to Koga for her to pursue her dreams and hurting instead. Even if there were no romantic feelings involved, which adds to the layers, thinking about their friendship, it's perfectly logic she wouldn't feel good saying "I want to be with you this day despite the fact you'll miss a great opportunity". So, she tried to play as she's not interested, but she considers the prom an important event for her, and Koga won't be able to be there.
People can be mad at Koga, but she's been going through a lot, and I think she's not good at getting the cues for Aya's feelings. So she thinks everything is going OK, since that's what Aya has been saying. Yet, she's getting the distance and that something is off, and she's not taking a more proactive attitude into figuring Aya out. That's probably the issue with her. She can't take hints, and hints are all Aya can give her without completely opening up and making it awkward between them. If Koga comes up to her and is reassuring about their friendship or relationship, than they'd probably work things out. And the prom? People here want Koga to go because if she drops the music appointment to go to the prom with Aya, that's an act that proves Aya is as important as music is to Koga. Romance *jazz hands*

I (aro ace) don't really understand what the issue is right now? Like isn't this a good thing? Sure she'll miss prom but this could be a once in a lifetime opportunity! And it's like a fancy party right? Just ask Aya if she wants to be her plus one!
Or does it not have anything to do with the party and it's just about the kohai?
I'm just not really getting it right now and reading the comments down here and seeing so many scream for Koga to just go to the prom feels strange to me?
Prom isn't really a big thing in my country so maybe that's what making this strange for me? ( ̄∇ ̄")