Just going by what I've seen the engineers say regarding the attack.
impast of a B-707
Which didn't weigh as much as the fully loaded aircraft that hit the buildings...according to the engineers.
The reason for having a sprinkler system was to protect the structure from a catatrophic event, such as the impact of a jet aircraft
Find me a sprinkler system that can deal with the amount of Jet-A which was suddenly introduced into the structure via airliners travelling at high speed.
What would an investigation into the un-licensed Middle Eastern plumbers working on the sprinkler systems in the WTC days before 9-11 hurt, considering the Middle Eatern plumbers are known criminals?