There are (at least) two major issues:
1. There is significant overlap in TV markets so it doesn't do much to bring in more media revenue, especially for the ACC schools.
2. Conferences with football and non-football schools cannot survive long term. We've been down that path before. Eventually, all the Big East schools, except UConn, get tossed aside. I'm not sure the non-football schools want to do that again. They, rightfully so, felt like second-class members when the Big East first expanded into football ~30 years ago.
An ACC-Big East merger would benefit UConn but I would be hard pressed to ID another school that would come out ahead.