If you turn on all of the fire hydrants, some of them aren't going to have water. Over a large enough network, with enough open valves, no matter how much water you have feeding it, you will run out of pressure. The end. Turns out, when you have fire spread out over an area that large, you meet those conditions. You can do the same thing with your household irrigation system, at a much smaller scale.
Now, if you're suggesting that the civil engineering standards should be updated to meet newer threats and resultant requirements, sure, I'd agree with you. But the water delivery system is not "bad"; it's built to a known standard that is, for lack of a better term, outdated. But that's still the standard.