Why do people replace personal specials?

I agree with you, I do find it strange as well like for ex. when someone replaces BK's / Zelgius' Black Luna for something like Aether whereas the original special has this discounted and more efficient Luna effect

However, they may have done it for a reason, like how their teammates have a special cool down reduction which enables that unit to perform a powerful special such as Aether in quick succession and can deal more damage than their original special etc.

Though I'd prefer to keep their unique specials

Gotta love that Regnal Astra

Arena scoring mainly...
Or trolling. you never know.

Frankly Regnal Astra should never be changed imo.

I've seen Aether BK and Zelgius a few times, and there's some reasons you'd want to do it. Aether provides consistent recovery, making them much more resilient during drawn-out battles. Additionally, I think Aether might score higher in the arena than Black Luna? I'm not sure though, honestly.

I'd use Black Luna 95% of the time though. It's just so strong.

Aether same score as Blak luna. Often its just overkill and he would prefer the healing, ive thought abput doing it before.

u should nvr let their specials cloud their potential. sure those specials make them feel more special then other units. but sometimes a mix and match experiment might lead to a sudden meta change giving them more flexibility in building when given multiple IVs. some might say everyones regnal astra makes her feel boring. making ayra predictable. it also makes arena more fun, u get to see completely new builds u would have prob nvr considered destroy ur plain boring off-the-book builds, or catch u offguard when u go to initiate thinking u would beat them normally

Team composition, set specifics, memes, and / or comfort. I personally prefer Aether on Zelgius for challenges and TTs I can just autobattle through (also helps for some super specific PvE maps); I also have Galeforce on Ayra, along with both blade skills, for the sake of memeing with Defense teams. If someone has a preference for a build, and it works for them, it doesn't make them weird, so just let them do them.

I like Aether on chains and tempest and forget to fix my skills after that.

After releasing of the Quick Riposte Seal, I never changed my Fjorm's special anymore. Just use that along her base kit and she will kill any mage she baits as long as her special is active. Better if she has a Breath skill.

Depends how they wanna run them, honestly. I switch out Dragonskin for everything but arena since I run her as a player-phase unit, not a bait unit.

And for Fjorm I don't like her special much, since you can't use it as a straight-up attack special, so I swap it with Iceberg for more all-round tanking. Those are some examples.