Because the amount of data alone would be so astronomical as to be very obvious. Unless it’s specifically recording you locally and then uploading that information when you’re on wifi (which would be obvious too because of the slow down it would cause, the amount of bandwidth it would take up (making you hit data caps with your provider and throttling your service), and the fact that most phones just do not have that much storage and don’t have a slot for added as cards anymore. Feasibly it doesn’t make sense for a handheld device to be recording everything you say passively. Your battery alone would have to last several weeks of normal use.
Because the amount of data alone would be so astronomical as to be very obvious. Unless it’s specifically recording you locally and then uploading that information when you’re on wifi (which would be obvious too because of the slow down it would cause, the amount of bandwidth it would take up (making you hit data caps with your provider and throttling your service), and the fact that most phones just do not have that much storage and don’t have a slot for added as cards anymore. Feasibly it doesn’t make sense for a handheld device to be recording everything you say passively. Your battery alone would have to last several weeks of normal use.