Is it simpler? Are fires set by angry people more common than fires that happen by neglect, stupidity or equipment failure?

That's not simpler because it throws up more questions. Who would want that, how did they get access, how did they plan it do quickly, how they know to target this specific one, etc.

Simple is: fires happen in buildings due to failures. There was a nonhuman failure like in millions of other cases. No need for a conspiracy.

Otherwise, with your logic, god explains everything because "it's simple"