What's Wrong With This Picture?

From today's jsonline: North Shore firefighters arrived at the scene to find fire in the back of the structure. The call later was upgraded to a second alarm with mutual aid fire departments responding form Thiensville, Cedarburg, Menomonee Falls, West Allis, Wauwatosa and St. Francis, according to Boehlke.
http://www.jsonline.com/news/milwaukee/46081187.html

Why wasn't the Milwaukee Fire Dpartment involved? They had St. Francis drive across the City of Milwaukee to fight a fire or staff a station. Engine 18 located at 3628 N. Holton Street, is just a short distance from the fire scene. Why can't the MFD cooperate with other communities? Just wondering.