Actual trained terrorists with experience at an organized training camp aren't going to have any actionable material on a laptop or cell phone. You have to be able to identify the dangerous citizens by other means.
The procedures performed by border agents give different puzzle pieces of the whole picture. When researching crime rings you always need to look at communication pathways, much of that information is stored on the smartphones. Why not pick it up when people are actually bringing it with them?
https://www.ctc.usma.edu/posts/how-terrorists-use-encryption