It may be simpler than that. Even if Snowden has walked away from this service, the publicity may have attracted a lot of people the authorities find interesting, including legitimate (whatever that means) persons of interest.
No, this has nothing to do with common criminals and everything to do with Snowden.
He shut it down because that was the only way to legally prevent the government from spying on his users.
http://securitywatch.pcmag.com/privacy/309277-judge-says-fbi...
I wonder why he didn't challenge it.