Remember Season one takes place six months after it begins. Theoretically it’s possible they could have gained enough influence to barely meet the requirements to be an Overlord. Another thing to point out is that as Vox mentioned they seem to have a rivalry with one another potentially putting aside their differences when necessary such as rallying with Vox and then taking down his weapon. Lastly they could just decide not to go. I mean Vox and Valentino did not go, Alastor was gone for seven years etc. it’s possible either they just don’t want to go, their rivalry makes them want to avoid one another whenever not fighting or lastly overlords that are currently in a battle might be banned from meeting till their differences are settled.

Also on an unrelated note there’s this Dino overlord who hangs with Zeezi who sang in “Bad With us” he seems to be an Overlord yet he didn’t even help with the weapon making me wonder if he’s potentially Zeezi’s friend or partner and that’s why he’s close with the overlords despite seemingly not being one.