As Chad Scott pointed out (HT EO) ESPN owes the ACC $45 million dollars this year if they do not launch the ACC Network by July 1, 2016. July is still far away, but I don't think the ACC and ESPN are going to rally and launch a network in three months. It looks like the ACC is going to get the money from the network without having an actual network.
The change in plans is very much due to the cord cutting phenomenon. And while the conference will lack the cache of having its own network, this is probably a better deal.