>>103608441
Different recruitment methods.
>Myth were just 5 random content creators who each ticked off their own niche, and all happened to debut for the company around the same time. They bonded over time once they got to know each other more, but it took time to get there, and by the time they were at full camaraderie, Gura, Ame and (for about a year) Calli were already looking at the door.
>Irys was thrown out there by herself and was stuck in limbo until she got handed Promise
>Council were forced into playing characters which didn't entirely suit them for the initial parts because of one dude with an ego who tried to upstage their debut. They had more time to build up initial connections, but only through video calls. Sana kind of served as the heart of the group, but when she tapped out early due to figuring out vtubing wasn't her thing, the other four just kind of spiralled now that all their plans had been trashed.

Advent and Justice got to hang out in person first and got to bond properly before making their debuts which meant they figured out what part they all played in advance and could debut already being able to play off each other.

And to be fair, it's kind of the same for the JP branches as well. The first gens were just random people who debuted at the same time. It was years before Gen 2 ever had an off collab, and at least two of them were late. Gamers worked because Korone and Okayu were already a pair before joining. It was only from Gen 3 onwards that the group were a unified unit before debuting.

The IDs just get along because they mostly all live near each other anyway, so just hang out all the time regardless. They are also never really expected to play into lore and characters as much as the JPs and especially the ENs, so just get to talk shit with friends without playing a part.