A couple of more points.
1) I'd bet that Fox's relationship with their Pac12 and Big10 partners is the driving force with ACC alliance. I'm not exactly sure what the ACC's motivations are but I would bet that feelers were made to Clemson and Florida State by the SEC and regardless of their relationship with ESPN... the ACC (and Notre Dame) was going to preemptively put an end to it by joining up with Big10 and Pac12 and controlling the college football playoff.
2) In the case of the Big East having zero leverage in aligning with the Pac12 and Big 10... they don't have much which is true because so much of this is football driven but the Big East is still a major partner with Fox and Fox wants to keep everyone happy. Also, if the NCAA tournament craters due to the SEC's greed, Fox would be in a position to capitalize with their own version of March Madness comprising of those 4 conferences.