Because things like SMS history and call history are far more valuable. They can download your entire SMS, call and contacts list, get the text from that, and then create a social graph based on who you know and who you are in contact with. Then it becomes very easy to trace people and who they are affiliated with. Plus going through SMS history is a great way to find reasons to throw someone in jail. My friend coming from Canada to the US was denied entry for 10 years even though she lived in the US most of her life because of jokes she had in her texts about marrying her ex-boyfriend for a green card. It's very real and it happens.