What It Takes to DIY HashiCorp's Terraform Cloud

>In this article I will describe the main aspects of Terraform Cloud and what the DIY equivalents for them might look like at the high level, pretending that ready-made tools for that do not exist (they do in fact; I am building one).

I like how companies are shelling out tens of thousands of dollars for AWS/Azure a month, but all the sudden there are people who want to write DYI projects to clone Terraform, given the fact that Azure & AWS have completely open source SDKs (backed financially by MS & AWS) that available in JS, TypeScript, C#, Go, Rust. Why ?