Unfortunately, it's not in manufacturers' best interests to make these devices hackable. All costs considered, Amazon is likely selling these near at-cost. They're not selling the hardware as an independent product. They're selling it as an extension to their larger platform (Alexa). As soon as a product becomes hackable, some portion of sales are lost to enthusiasts who buy one thinking they might hack it some day. If this gets out of control, eventually the company is subsidizing enthusiasts and the whole proposition becomes a net loss for the company.
Amazon knows voice agents are on track to become a primary human-computer interface, a user agent for the internet, and Amazon wants to own a big share of that pie, because that is a gatekeeper tech. Those who own it can ensure people buy on their marketplace, and companies that want to sell to these consumers must pay a fee. Amazon can't reasonably compete with google or apple in the "voice agent on the smartphone" segment until some antitrust forces those to offer a choice of agents, so they do the smart thing: push hard for a quasi monopoly on ambient microphones.
Over time there could be an antitrust to tell Amazon they must open "their" voice agent infrastructure for the competition, and they will use this "investment" as an argument why that would be unfair to them. Even if, they will rather add an API limited to accredited competition instead of giving consumers root on the hardware.
The whole concept is hostile to the consumer by design: imagine a keyboard would include a non-replaceable typing agent that can only type on websites that are partners with the keyboard manufacturer (as in "buy the skill for your keyboard to type on HN") and all your inputs are first sent to the manufacturers servers. Hey you get auto-complete and the keyboard is cheap. That is the state of voice agents.
I'm pretty in favour of requiring some level of "the user can run whatever they want, supported but at their own risk" for every (reasonable) device for exactly that reason.