Duke has to keep its options open.
The ACC is toast if the projected defections happen. Seven current ACC members; Clemson, Florida State, North Carolina, Miami, NC State, Virginia, and Virginia Tech are exploring options with Florida State and Clemson already suing to escape.
On the other side The Big Ten wants Notre Dame and has already annexed about every single Irish rival except Stanford. They are now in perfect position to take both.
Virginia and North Carolina are the top prizes bolting from the ACC because of their media value and are highly desired by both the Big Ten and the SEC.
There will be a mass exodus of remaining schools applying for Big 12 membership if Stanford, Notre Dame, Virginia, and North Carolina all accept their forecasted P2 invitations.
This will leave Boston College and Wake Forest with the Washington State/Oregon State dilemma; owning a legendary conference name but without any media contracts, and Cal and SMU relegated to the discard table again.