Absent a set of keys, the government cannot open digital communications protected by strong encryption. Thus, for such communications, the government cannot prevent, or even detect, criminal activity. Before the creation of strong encryption, our government could look just about anywhere it wanted to, so long as it had the proper authorization. We allow these intrusions upon our freedom and privacy in exchange for a desired level of protection or security from our government. Practically speaking, nothing prevents the government from accomplishing these searches, no matter how hard one tries.
Encryption changes the equation.
Even once having obtained proper authorization to search or tap into digital communications, strong encryption completely blocks such efforts. There is no way in. As some have suggested, there is not enough computing power in the universe to break this encryption. For obvious reasons, the government is annoyed and quite concerned. The government contends it must have the ability to monitor all digital communications, whether encrypted or not, or else it will not be able to detect, let alone prevent, criminal use of digital networks.