The government does not need a warrant to gain access to your information, easily evidenced by mass surveillance of the world for the past 15 years. If they really want something you have, they will just take it mobster style and tell you to go fuck yourself. They don't have to charge you with a crime, they can charge your property with a crime and force you to deal with a kafkaesque process where your property is guilty until proven innocent by the people who issued the very order to seize it. Information + Encryption is one of the only things regular people have that is resistant to this process.

They do need a warrant for any information to not get laughed out a US court though. This is the main reason they are going after the data this way, because they want what they found and know wouldn't survive discovery to eventually be admissible as legally obtained evidence. That and it will set a nice precedent for them to deputize private persons and corporation into being law enforcement when they just can't be asked to not fuck up one simple thing.

This is also not-coincidently a case likely to polarize people against Apple with the old faithful terrorists are coming to get you rhetoric. A most slippery slope indeed, nearly guaranteeing that everyone who is supposed to be checking the executive branch for overreach will just go along with them wholesale.