I've always thought that along with the BCS issue, BC was desperate to get out of the Big East to avoid having to play UConn. BC's approach to athletics is to position themselves as the big-time college "franchise" in New England; they were just about there, briefly, but then UConn blew by them in basketball, and was threatening in football. (It's OK to not play, as long as UConn isn't actually ranked -- BC football was a weak second to Dartmouth for many years and nobody much noticed.)
BC's recruiting is much less regional than it used to be -- it's still a factor, of course, but I think only a piece of a larger business plan. That marketing arrangement with the Sox is significant.