People who think that there’s no way that Google and Amazon could be recording everything need to realize that this is also not true. Most of these “limitations” are software enforced, and that software is updated constantly.
I also don't necessarily assume mal-intent on the part of the companies, but that doesn't mean there won't _ever_ be that intent. Trusting that all of these assumptions hold over time is hard.
This is the big point. You are not only trusting that the company as it is today is doing the right thing, but that the company will continue to do the right thing for so long as the device is in your house - and that they will do the right thing in perpetuity with your data (including if/when they sell the company down the road).
This is a problem with forced updates in general (I'm also thinking of Windows, Chrome, Chrome extensions, etc. here) that security experts seem completely blind to.
That said, note that even if the software didn't update, it doesn't mean it would have to send bad packets when you're actually observing. It could randomly start doing that once in a while after a few months.
(It's true of cell phones too, of course, and I am engaged in constant activity to ensure the phone works for me, and not any of the many corporations that want to make it work for them. Turning off notifications, uninstalling certain apps after they've gone bad, ensuring permissions aren't too wide open, uninstalling default-installed apps and disabling others... it's a constant battle made worthwhile only by the fact that in the end, I really have mostly mastered my phone and it is working for me. I don't have one of these audio assistants because it is far less clear to me how to do that. Modulo being spied on by intelligence agencies, anyhow, although at this point I'm not sure how one could even escape that.)
As a side note, whataboutism adds nothing of value to this discussion about the Google Home and Amazon Echo.
Also, talking about your contradictory behavior with your smartphone isn't whataboutism, unless you want to avoid addressing your hypocrisy, because smart phones are susceptible to the same blanket fears you have with homes/alexa. To critique only the latter, and not the former (which you use daily), is not fair.
Per Google's own site: "Long press to trigger the Google Assistant."