That's so ridiculous I'm not sure how to reply or even interpret your comment.
Of course, the cost is built into other services. As pointed out, AWS can get very expensive for many use cases, and that's exactly what you're paying for: access to managed services.
Beyond that by developing on AWS you are taking steps to lock yourself into using their system - your configuration isn't portable to other services. So the time/manpower you spend configuring AWS-specific things is another cost associated exclusively with its use.
> a server running on a computer device, listening for requests at a particular port over a network, serving web documents (HTML, JSON, XML, images), which serve in solving specific domain problems over the Web (WWW, Internet, HTTP)
Clearly IAM is a service.
Further, the service needn't operate on resources called "instances" in order to provide value--few AWS services offer "instance" resources and yet they deliver value to customers and are consequently priced. IAM isn't priced directly, but rather the operating cost for the service is built into other AWS services, presumably to encourage people towards security best-practices (charging for IAM might dissuade users from building securely).
The biggest example is probably IAM, which makes it easy to control which servers can take what actions on which other services. And can also be integrated directly into external tools like Vault.
Want to use service discovery? No need to set up Consul/Istio/etc., just use the managed service. Same with load balancers, and VPCs, and SSM, and route53, etc.
Sure, in 2020 none of those services are that hard to replicate pieces of, and open source tools abound. But setting up those tools all takes time.
Only other nit is that the article makes it sound like Terraform and IaC is meant to abstract away AWS vs GCP such that one terraform module _could_ be deployed to either just by changing some string value from "AWS" to "GCP". I don't believe any serious (and good) efforts are being made in that space, and you won't find any popular modules like that on https://registry.terraform.io/.