Existing wiretap law is almost 20 years old and doesn't capture the nuances of modern internet use. The Communications Assistance for Law Enforcement Act was first authorized in 1994, and it ordered "telecommunications carriers" to comply with court orders to assist in intercepting communication. Since then, communication online has taken off, while the landscape of what we know has telecommunications carriers has drastically changed. In 2006, the FCC expanded the act to include Internet access providers, but there's a tricky caveat: court orders under existing law only instruct internet communications providers to offer technical assistance to law enforcement. That gives the tech companies some leeway if they're uncomfortable handing over information; they can just say they were unable to make the technology work the way the FBI wants.