Anyone know why there was no fire suppression system in the roof area?
As far as I understand it, for safety reasons, there was no electricity in the "forest" (the nickname of the wooden structure that held the roof)
As to why the roof collapsed as it did and not the scaffolding, the roof was made of lead (210 tons? quoting from memory). Melting points, melting points, a bit more than 320C vs around 1500C.
As I said earlier, in those cases, apparently, the policy is to work from the inside, for a bunch of reasons, including additional damage caused by water, and also that you don't want to push the fire back inside: that can both increase damage and cause massive bursts and fire expansions because of the typical airflow in those churches.
The airdrop issue has already been covered, the last thing you want in those cases is too hit a critical pillar or face of the building. One other thing is that the water dropping planes are mostly based in Southern France, where forest fires are more frequent. They would have taken several hours to reach the cathedral and did not have enough time to reach Paris, plus no convenient place to fill their tanks. Finally, with fire-fighters inside, it is probably not a good idea to drop 4 tons of water on their heads.
I did find a link to PDF documents by the company that cited its renovation work on the cathedral as a reference. Unfortunately (and unsurprisingly I'd say) those links are dead.