Why would they leave yacht money in a warehouse doing nothing?

A fire suppression system can only do so much. Having said that, I wouldn't be surprised if they had none or it didn't work. It's Russia, after all.

There was a (probably accidental) fire at a smaller warehouse of theirs in early 2024 which burned for a day and cost a shit ton of money, and - shocking - the building had never had fire or safety inspections. So yeah.