Why are fire sprinklers and extinguishing systems failing?
If you're not from the wildfire west, it's hard to get it.  This isn't a dumpster fire, it's a firestorm.  You might as well be putting the building in an autoclave and expecting it to not burn. 

Anyway, sprinkler systems do protect buildings, but from the normal scenario of fires started inside occupancy space.  The goal is to suppress it before it heavily engages the building.  When fire is consuming the rafter holding the sprinkler pipe, it's much too late, and wildfire attacks sprinklers from the wrong side. 



Far and away the #1 defense in the firelands is defensible space. Keeping vegetation (fuel) down to bare minimums within 100' of any buildings. When people follow the rules, they tend to do dramatically better.  This is one reason you have random vineyards relatively untouched - this is the heart of California wine country, some say best wine in the world. 

The problem is, homeowners and landscapers absolutely hate defensible space, and either neglect it or actively ignore it. 

Google Earth tells the tale; fire up Google Earth on the area and go see how well they did with the 100' rule.  

Worst of all are eucalyptus trees; these were imported from Australia because they are fast-growing and were thought to make good windbreaks.  They are an extremely oily tree with very high fuel value, and they go absolutely crazy in a firestorm.  For some reason, Californians just love the distinctive smell and love to landscape with them.  Makes no sense. 



It's true that endothermic building materials help (materials which aren't fuel). But that only takes you so far; occupant contents are often highly exothermic, which is what finished WTC.  That can be managed in a hotel with good furnishing choices, since hotel guests don't bring much and will take it with them when they evac.  

If I were trying to build for wildfire survival, other than defensible space, I would go for reinforced concrete construction with non-flammable insulation on the outside, with non-flammable cladding designed to keep the insulation intact. These also happen to harmonize very nicely with passive solar design, which is precisely my point: the big insulated thermal mass that resists day-night thermal changes, will also resist the fire's heat. 

Another scheme, an amplification of the above, is earth-sheltered design, in which case you could let the fire roll right over the building. 

There would be a place for water in defending from wildfire, but you've got a big sourcing problem because everyone will want water at the same time, and you're already in a desert. Wine country wasn't a desert, but it became one when a million people moved in.  California water supply is a big-dam problem, so you would have to have a local supply of some kind, e.g. a pool.