One big thing not mentioned here: the massive collection of managed services AWS gives you at no cost.
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/.