You don't think they do, but Cloudflare estimated AWS' markup is 7959% here https://blog.cloudflare.com/aws-egregious-egress/
The $/Mbps prices there - about $6k/Tbps in the US - are based in reality and are absolutely reflective of what it costs, hardware, software, redundancy and all - for an effectively 1Tbps pipe.
If you're pricing as $/GB on top of that capacity and keep it reasonably heavily utilized—which can be hard given diurnal demand—the margins only get better! Products like Glacier (S3) exist to fill exactly those gaps.
(Note: currently work at Cloudflare, but wasn't part of this blog and I've been around a bit...)