It puzzles me that they (apparently) can't make San Diego work from Atlanta. Atlanta is a far, far larger market than Milwaukee, they are far more established in ATL, and they have a much larger hub there to feed it.
Yet they doubled-down on MKE-SAN, where fare pressures are greater and the hub is smaller. Last summer AirTran's average ATL-SAN fare was $156 but MKE-SAN averaged $119. That was with no nonstop compeition. I don't see the average fare on MKE-SAN going up significantly this summer.