Because they involved your account in the crime and also, according to you (Zhou Tong) used it for credit card fraud. People file police reports for much, much smaller thefts. Insurance companies have people file reports as a sign of honesty. Lots of reasons to file a report.
The hacker didn't steal from me. Why should I file a police report?
The credit card fraud isn't for me. He used someone else card to buy stuff and ship to a freight forwarder. And he entered that email address for the order.