There is a limit to the height that water can effectively be pumped. That may be the reason.
www.slate.com/articles/news_and_politics/explainer/2004/12/how_high_can_a_fire_hose_shoot.html
"^Between 75 feet and 100 feet straight up, depending on water pressure. In practice, though, firefighters on the ground rarely attempt to reach higher than 40 feet with hoses. Since water pushes smoke and heat back into the building, attacking a high-rise blaze from the outside can actually be counterproductive. That's especially true if there's a chance people may still be trapped inside.^
Firefighters can also use truck-borne ladders to reach high places, but scaling a ladder with a heavy hose is often difficult. The general rule of thumb is that ladder-and-hose setups are only effective up to about the 10th floor; after that, it's imperative that the blaze either be fought from an adjoining structure, such as the Chicago building's roof wings, or from the inside.
^The most common approach in high-rises, then, is to use a building's standpipe system. This consists of an interior vertical pipe that runs from the ground to the roof, allowing firefighters to connect hoses on any floor. The water usually comes from either a fire truck or a street-level hydrant; firefighters connect a hose from the water source to a standpipe outlet, and it's then pumped upward to the blaze's location.^"