In a city of 800,000 people and a metro area of nearly 2 million, Obama cannot even fill a 70,000 seat stadium with willing spectators. I think they realized it would have taken way too many buses and a lot of free sandwiches and malt liquor to pack the stadium. Would have been a security nightmare.
Reminds of the the scene in Dickens' Christmas Carol where businessmen only agree to go to Scrooge's funeral if a lunch is provided.