Sprinkler heads on fire suppression systems go off locally - if there's a fire, then only the sprinkler heads in the vicinity will go off. The alternative is to let the fire spread and destroy the entire facility.

But in addition, this particular story takes place in a skyscraper in Manhattan, with the data center in question occupying a portion of one floor, with office space surrounding it. So letting a fire burn would create significant risk to human life as well.