An important characteristic of both crimes and fires is the impossibility of knowing where either will occur. Firemen may have a general sense of the buildings that are at a higher risk of burning down, but they have absolutely no idea about which particular house will be the next one to catch fire (unless the firemen are the arsonists). Similarly, cops may have a general sense of what neighborhoods have a higher crime rate than others, but they have absolutely no idea which person will be the next one to commit murder or rape (unless the cops themselves commit the next murder or rape).
Given that cops and firemen are both concerned to respond to events that cannot be predicted, it is extremely odd that they act so differently from one another. Firemen do not "patrol" neighborhoods in the hope of spotting the next house fire or car accident. They wait until someone calls them, and they respond accordingly. Cops, on the other hand, do "patrol" neighborhoods, hide under overpasses, dress up in "undercover" costumes and otherwise skulk about their communities looking for crimes that are being committed.