From the plaintiff's response to this motion linked elsewhere, I'm thinking that Disney is somewhat compelled to file this motion in order to have any shot at arbitration being relevant at all. Their initial response to the lawsuit (included in the appendix of that plaintiff's response) is a pretty stock "we don't think we have liability here, it's on the restaurant" response. But the plaintiff response notes an aspect of law where a party willingly participating in a lawsuit without asserting their right to arbitration early is presumed to be waiving that right. So it sounds like Disney must produce some argument early in the proceedings that this should be removed to arbitration in order to preserve that possibility assuming that it is something that would be covered by the arbitration agreements.
I'm not sure I buy how they connect their agreements specifically to transactions in this publicly accessible mall, but it seems like if they didn't make the attempt at all, they couldn't later make the attempt if later in the court process something came to light that indicated this should have been handled with arbitration.