This makes no sense
The only reason I can think of for Amazon to refuse this is if they actually record AND STORE everything it hears 24x7, and save it indefinitely. If they're really doing that, I can see why they wouldn't make to make that known by producing this evidence.
If they are doing what you would think is reasonable, and tossing anything it hears that isn't intended for it, then Amazon could say "sorry coppers, we aren't selling an always-on spy device so we don't have the data you're requesting!"
It is one thing to SUSPECT that companies like Amazon and Google are saving everything a device like this hears forever, quite another to have it essentially CONFIRMED! Hopefully this case will get lawmakers in a tizzy on both sides - the ones who want unlimited police powers will want laws that force Amazon to comply, those who don't will try to instead fix the problem by requiring companies that make devices that act as a 24x7 bug note it prominently on the packaging!
Maybe this would be a place for cooperation - make a law that says if you sell an always-on recording device that you must give up the data if presented with a legal search warrant, AND you must prominently label the device with a notice that it saves everything it hears. Let's see how the Amazon/Google business model for these assistants holds up with that labeling forced on them!