I blame it all on the greed and avarice of the SEC. It was the SEC that first took advantage of the rules' loophole (not intended for P5 conferences) which allowed a post-season championship football game for conferences with twelve members. The resulting expansions have been so detrimental to intercollegiate sports, IMO. And, if Syracuse fans miss the old Big East, there are those of us who miss the old ACC. The ACC of the 80s and 90s was every bit as good as the BE of those decades. Expansion put an end to round robin scheduling in basketball. In the 70s and 80s, fans from most of the ACC schools could make day trips for away football games. College Park to Atlanta might have been a stretch, but the rest were doable. (When I was in school, teams took a bus to away games.) Now you have to fly to see some away games.
WRT to MSG and recruiting NYC: The ACC schools never had much trouble recruiting elite talent from New York, New Jersey, and Pennsylvania. There was a steady flow of recruits heading south. And, if you're old enough, you can remember when the BB powers of the northeast didn't need the BE or MSG to recruit well. Recruiting has changed significantly, but it has changed for everyone, and I don't think the change had anything to do with changes to the BE. The AAU and the emergence of prep schools focusing on basketball have altered the direction of the recruiting spotlight. The AAU circuits have changed how prospects are evaluated, and, increasingly it seems to me, the best kids are leaving public schools for places like Monteverde, Word of God, and La Lumiere. Admittedly, there was a time when the likes Oak Hill and Flint Hill did similar things, but the scale appears to have changed. It also seems to me (and I could be very wrong here) that many of the old inner city parochial school powers are either closing or de-emphasizing basketball.
I get it that the move to the ACC for the old BE schools hasn't been especially easy or productive, but I doubt that there were any other viable alternatives.