The only difference I see is that the battery of a smartphone would drain rapidly if it was constantly recording and uploading the recordings to the cloud. But you are right, a smartphone is a device used to monitor you and people whose freedom depends on that knowledge, like radical political activists are aware of that. And yes laptops are exploited. To give an example: The German government has developed a number of trojans for Windows over the years and the BKA routinely uses them for targeted surveillance.