Because just like back in Teyvat... we're officially enemies, even if you're still my friend. If I couldn't get you to join the Fatui, there's no way I can get you to join the Kenoma.

[ he avoids the part about where he basically initially joined the Kenoma to keep her protected while she fought off its influence. ]

I'm supposed to bring anyone I find here in the shrines back to the Regent ... [ but obviously he's not going to do that with her. ]