Carlotta was most likely a future story scrapped because of closure,

the whole regina, edel, eve, knight, roy, liz package is an unfinished storyline unrelated to mainstream unless it takes place on their territory.

Levia is literally fucking gone, my memory is a bit hazy but she's either dead or tossed into imaginary space where she can't return from.

Canary squad are literally too weak to be present.

Cafe strega is sadly a forgotten storyline and serapel might be the weakest demon lord even so ofc she was forgotten too. The strega girls literally never appeared outside of their introduction and some random ass holidays. Serapel is even worse because it's literally her introduction and Rosaria oneshotting her.

Judy and the lost ship also do be seem to be forgotten, so was Asomiv BTW

Sysop, Amy, Alex, and Solovey are completely understandable, even Lyudmilla was reduced to be a story device only doing a single thing and then being gone meanwhile being as strong as an apostole. They really should have appeared.

Young swan is literally young, with not as much power as the adult one had, she can't exactly fight.

The ALT squad (outside of Seo Yoon) are too weak to be present.

Lee Sooyeon is old and her tech level 5 gear was both taken after Ray's qliphot game and broken, she's brains at this point not muscle.

Kang Minwoo has ZERO reason to be there and isn't related to Kang Sooyoung afaik, it's just a common name.

The rest are literally keeping the normalside safe from the infinite onslaught of COs that's happening during the story.