It's like going to a restaurant and complaining about the price of steaks because beef should cost a lot less. There's a ton of other things involved, and yes, they probably have a decent margin, but not as much as you initially imply.
So they should be able to reach the lowest amortized cost for bandwidth with all of those costs included.
They price bandwidth so high because they can and they are still growing.
so, when should we expect this gloriously efficient competitive market to kick in to action?
my guess is that the AWS ecosystem, despite "price gouging", is simply the best and will be because this is really hard, non-glorious engineering, where solid reliability actually matters. anyone who wants to can go ahead and co-lo, so, whatever. people who want cloud will pay, and those who can't or won't, will not.
It's easyish to compete on bandwidth costs, but Amazon has a lot of other features many people want; it's harder to replicate all of those, especially the part about having a long history of operating such services and not making a lot of changes to make things more expensive or otherwise more difficult. Having to pay a much higher than market price for an easily replaced good in order to get a good that's less easily replaced is textbook anti-competive bundling.
If your bandwidth usage is high enough, maybe it makes sense to send it all through AWS direct connect, and pay for transit yourself; although even then, the AWS direct pricing seems a bit high.
And it's easy to replicate the water part (after all VPS providers are dime a dozen), the hard part is the food.
The point is that if you charge absurd prices for what has basically no marginal cost your pricing model is broken and 1) you are excluding customers that are particularly sensitive to this price or 2) you are liable to undercharge other customers that primarily use other services for which you are not charging what it costs you to provide.
For AWS, given the generally inflated prices, it's probably a lot more of 1) than 2).
There are plenty of other platforms as well, like Digitalocean, that have much lower bandwidth pricing.
Nobody else can give you bandwidth out of Amazon data centers. Amazon's advantage is having a ton of services that work together, and they take advantage of it to price gouge on bandwidth.
If you're buying a standalone CDN service you can get massively better rates.
Really this is the secret sauce of the cloud. Create new abstraction layers where you can charge for logical separation on a physical basis. First VMs, then containers, then serverless... Would be cool if somebody did it with bandwidth (looking at you, Cloudflare). Why can't I buy an elastically sized pipe? Why do I need to pay for the stuff I put through it instead of reserving a size for the time I'll need it?
[0] https://twitter.com/eastdakota/status/1371252709836263425