In what way is AWS a monopoly. They have a ton of competition in every aspect of their business.
We can see this when researching the books as published to shareholders. When AWS was the "sole" player (first mover advantage) they had insane margins. Then competition stood up: GCP, Azure etc. And grew. Their margin has staid the same. And is roughly similar to that of GCP and Azure. Which means they either have secret gentlements agreement over pricing (highly illegal, not likely, the risk is just too high) or there's other mechanisms at play that allow them to keep dictating the price.
Cost of switching is very likely such a mechanism. They lure you "on board" then once you start feeling the pain of the high margins, there's simply no way you can move to a competitor with lower margins - either that competitor isn't one really (Digital Ocean, OVH, Linode) or these competitors aren't competing on your margin (GCP, Azure) and have similar margins.
As a baseline, moving production workloads that run entirely on VPS or physical servers between datacenters is already a very high cost/high effort task.
Anything you do to make the architecture more complicated is going to increase those costs.
All AWS (and co) did was offer a platform for building complicated architectures. The market response was overwhelmingly positive, and entire new engineering disciplines sprung up around managing and building these new complicated architectures.
Migrating them is typically rather difficult and high cost, but everybody knew this from the beginning, and this is what the customers want. The PaaS providers could maybe do something here or there to make it easier, but there’s nothing they can do to address the fundamental problem.
I guess the UK has different laws, but here in the US it works like this:
* 50% and below means you are definitely not a monopoly unless there is some weird set of facts than SCOTUS couldn't imagine the last time they considered monopolies.
* At some threshold around 60-70% you might be a monopoly, but market share alone isn't enough to prove that.
* Around 90% you are presumed to be a monopoly unless you can provide some very good evidence why you are not.
That said, the current argument is that because AWS is part of Amazon at large, it can gain undue advantage by being subsidized by other organizations in Amazon, and forgo profits in order to gain a controlling share in an industry.
This is basically Lina Khan's whole argument [0]
I personally don't subscribe to this argument as a major reason for AWS's dominance compared to Azure in the early 2010s was because of stronger execution (lots of training sessions, evangelization, some truly cutting edge architecture) and better product-market fit, but Hipster Anti-Trust assumes a bunch of smallish companies competing with each other can result in a similar outcome (hence why VCs like Thiel, Horowitz, and Andressen tended to support scholars affiliated to the New Brandeis Movement)
[0] - https://www.yalelawjournal.org/pdf/e.710.Khan.805_zuvfyyeh.p...
Some of the more "fundamentalist" members of that movement want de facto single product companies, with little to no consolidation/M&A.
Hypothetically good if you assume small players can compete optimally, but in action this absolutely means significant inefficiencies, at least in the tech industry because all small players inevitabely try to become large players in order to optimize on margins via economies of scale.
This CMA was investigating amazon's possible monopoly on cloud. So, this whole thing started rolling exactly because authorities are asking the exact same questions as you "In what way is AWS a monopoly." and in doing so, see enough leads to at least ask for reports and AWS's reply.
https://www.ftc.gov/news-events/news/press-releases/2023/09/...
Edit: Amazon, not AWS. Sorry for the confusion!