From 2020 to 2024, there were an estimated 1,544 warehouse fires [in the US]
That's an average of 386 per year/1.02 per day well before the recent fire that had a direct connection to Luigi-thought. Since then I don't think I've seen any others where there's a suspect with a message. The background incidence rate is too high already in a country that has only gotten worse economically since 2024. I'd expect it to increase from insurance fraud and undermaintained/vacant buildings. I'm staying agnostic on it being a new trend until more of these are connected to some kind of statement.