I imagine it works well for the whole business that they allow product teams to use the best cloud tools for the job rather than requiring them to use AWS for everything. If AWS is forced to compete even for Amazon.com's custom, that should make the whole company more resilient to long term technical stagnation.

That's how good Fastly is. Outside of this issue it's a great service.

Why?

Good to have 3rd party redundancy, time to fail over to something else now I'd think though.

really, m.media-amazon.com seems to have a very short TTL (showing 37 seconds right now) and has been weighted to cloudfront now.

Amazon is also known to use Akamai. Sure, Amazon relies heavily on AWS, but why should it surprise anyone that a retail website obsessed with instant loading of pages decides to use non-AWS CDNs if the performance is better.

Even if CloudFront became the default, I'm certain amazon.com would keep contracts with fastly and akamai just so they can weight traffic away from CloudFront in an outage.

AWS is almost never reporting issues on this page.

AWS don't report outages until it's undoubtedly them.