I wish conspiracy theorists out there would look up something like 'ruined cathedrals'...
They were made to be beautiful as a testament to the glory of God, nobody had sprinkler systems them, much less modern plumbing.
But sprinkler systems were not going to help for a roof fire.
The town I went to junior high and high school in had a huge fire in 1975, it started on the gym floor that had just been resurfaced. There are some things that just happen. Electrical wiring fails. You don't casually store or throw away rags soaked with volatile liquids (linseed oil comes to mind), it can spontaneously combust and this has caused so many fires but it doesn't occur to the user.
One really fortunate thing is that the fire alarm system was working and evacuation happened well before the visitors could actually detect that there was a real danger...I've heard people saying they were surprised and didn't at first believe it wasn't a false alarm.
As for guessing about conspiracies, it just burned yesterday. Nobody has had time to investigate anything and it takes time. There is no time for Sherlock Jrs. wanting attention.