How much computing power do you think it takes to approximately recognise a predefined word or phrase? They do that locally, on device, and then stream whatever audio follows to more powerful computers in AWS (the cloud). To get ahead of whatever conspiratorial crap you're about to say next, Alexa devices are not powerful enough to transcribe arbitrary speech.

Again, to repeat, people smarter than you and me have analysed the network traffic from Alexa devices and independently verified that it is not streaming audio (or transcripts) unless it has heard something close (i.e close enough such that the fairly primative audio processing (which is primitive because it's cheap, not for conspiracy reasons) recognises it) to the wake word. I have also observed this, albeit with less rigorous methodology. You can check this yourself, why don't you do that and verify for yourself whether this conspiracy holds up?