To be fair given what happened to Ynnead in canon with the ritual getting interrupted and the backup plan involving the croneswords running into the problem of "the last ones hidden inside She Who Thirsts palace", it would be understandable why the Clown god would prefer that anyone trying to godforge has as much of the Diaspora backing them as possible.We'd have to find the library first.
And we are probably going to be told "no, you cant go into the god forging section. That area needs the aeldmoot to approve of you entering it."
Having a significant portion of the entire Eldar military protecting a moon is much easier then having to invade the domain of chaos god (especially since invading Nurgle's to free Isha is pretty much already on the docket).