According to Computerworld, the suspect attempted to steal money from the online bank account of a Texas resident, and the FBI discovered the IP address but not the identity or the physical location of the attacker.
U.S. Magistrate Judge Stephen Smith rejected the request on several accounts.
For one, the IP address could have been (and is likely) spoofed, so the FBI could end up spying on an innocent user. The same unwanted result can happen if a computer is used by multiple persons, especially if it's accessible to the general public or is a work computer.
Secondly, even though the FBI said it would only take pictures via the built-in camera and not record video, the judge deemed that "in between snapping photographs, the government will have real time access to the camera's video feed," and that that was in effect video surveillance.
Thirdly, the information they wanted to gather is not located in the cloud, but on a computer that might turn out to be located somewhere where U.S. laws don't apply and where U.S. law enforcement has no jurisdiction.