Cincy and Xavier are in the Cincy market....not Dayton. LaSalle, Villanova, Drexell and St. Jo are in Philly. GW, George Mason, Maryland and Georgetown are in DC. Loyola, Towson and UMBC are in Baltimore.
DC and Baltimore are not the same city or the same market. Georgetown does not carry Baltimore because they are within an hour of each other.
But, even if they do cross-over....there are plenty of cities with more than one school...so, it shouldn't be that big a factor, regardless.
Dayton is its own market, but its small (#57) so its fans/alumni claim Cincy as their secondary market (like how San Antonio claims Austin when trying to list why they need a NFL team).
The Baltimore-Washington metropolitan area (#4) is the same market like Dallas is in the same market as Fort Worth.
The Big East want new markets that fit in the list below.
Omaha, Milwaukee, Chicago, Indianapolis, Cinncinati, Washington DC, Philadelphia, New York City X2 (1 is in NJ), and Providence.
Notice that that their are no duplicate states? And the only duplicate market is NYC (largest market in US, 4th worldwide) and even then they only have 1 school in each state NY/NJ.
This is the reason Dayton most likely won't be getting in, because besides being ridiculously close to Cincy, its also in the same state. If Dayton was closer to Cleveland they might have had a better chance.
Other Northern(ish) markets that could work would be:
St Louis, Kansas City, Minneapolis, Louisville, Detroit, Cleveland, Pittsburgh, Richmond, Buffalo, Hartford, Boston
Fan of the Big 12 Conference, the Mountain West Conference and...