Your point? We don't have 1:1 ratios between water tanks and hydrants. Many hydrants to one tank. They could've been dry because the tank was losing pressure due to other fire fighting efforts.
City officials came out and said there was a problem with keeping the tanks replenished. (hence dry hydrants)
It looks like an infrastructure problem for the dry hydrants. I'm sure it has been a big risk for decades. Probably because A) they hadn't had the worst-case-scenario we're seeing now, B) it would be extremely costly to do, C) it would be extremely time consuming and potentially disruptive to city life.
Basically all the same reasons an old bridge is left in place. (until it starts falling apart)
Fire breaks would have had limited effect in this scenario give you had extreme winds raining down embers on houses near the ocean from the hills 100s of feet above them.
They do clear brush and have ordinances surrounding this issue. What evidence do we have that this was a big issue?
But this is what you were dealing with. (see below) Clearing the hills of brush was not a feasible thing to do. LA made a mistake when they allowed people to move out into the hills.