Subaru's excuse is that they're both just TOO busy and their schedules never align, but what has Maimoto even been doing that's got him so utterly tied up he can't collab with Subaru, but is in a collab every week. I don't believe her, and I don't believe him, he didn't even include her in his Koshien team this year when Subaru doesn't need to be free or present to have her character made, just a simple approval on Discord.
But what do I know, I'm just a gossipper chatting at the watercooler.