UNC has posted an unusually candid announcement here on the Law School's homepage:
You may have heard by now that Professor Erwin Chemerinsky has declined Carolina's offer to be the next dean of the School of Law. I deeply regret that this is the case, but I also want to reassure everyone that we are moving forward. Provost Shelton made an extraordinary offer that would have allowed the next dean to do wonderful and important things, especially when combined with other external support. In fact, I believe that the scope of the offer from Provost Shelton is unprecedented at Carolina. It represented a meaningful commitment to advancing the interests of the Law School. Professor Chemerinsky ultimately decided that the resources were not adequate to achieve his goals for the Law School.
One might wonder whether making the grounds of Professor Chemerinsky's decision public will make filling the post easier.