At least there's some competitors now, which could be used as drop-in replacements if Let's Encrypt were to disappear.
I suspect the vast majority of certificate authorities will implement the ACME protocol eventually, since the industry as a whole is moving towards certificates with shorter expiry times, meaning that automation will essentially be mandatory unless you like manually updating certs every 90-180 days.
I think they're pretty different cases.
Amazon's one was essentially a side project for them, likely fully funded in-house using their R&D (research and development) budget.
In Nate's case, it was their entire product. They received funding from investors purely for the AI functionality that didn't actually exist or work. They specifically claimed that it did work, which is how they got the money. They spent all the investor money and had essentially nothing to show for it.