I'm not intending to defend Amazon but as a general statement about ISM bands: there are regulatory limits (output power, duty cycle, etc) on these bands. The output power limits are meant to limit the propagation distances from isotropic radiators.

So for Amazon's (or any) system to swamp the ISM band(s) they would need to absolutely saturate an area with their radios. That would end up running at cross purposes with their network since their own base stations and user devices would end up interfering with each other.

While I don't trust Amazon to do the "right" thing I do trust them not to step on their own toes.