Obviously there's a lot of flammable stuff in a Home Depot store, but wouldn't they take that into consideration when designing the building fire protection systems? What could have gone so terribly wrong?
You are assuming the sprinkler system was designed for the occupancy and no changes had occurred since it was installed in 1977. My take as a firefighter and insurance engineer who evaluates sprinkler systems. The sprinkler was not discharging enough water to control the fire. A very common problem, about 50% of the warehouses I visit sprinkler protection is not adequate because the stock changed but the sprinkler system did not.