I don't know why it is so hard for you to understand. Right now the Big East makes decent money as a basketball conference. There's the value. Merge with the ACC and the value probably goes up because in addition to the vaunted DePauls, Butlers, and BCUs you are adding games between UConn, Syracuse (God help them), Villanova, Duke, Marquette, Pitt, etc. There was a time when they were the two best basketball conferences in the country.
That's in addition to the value added by combined programs in Soccer, Lacrosse, Field Hockey, Golf, Tennis...