Can't tell if asked honestly. Because that's how most platforms handle their pipelines. Terraform or Bicep let you use a declarative language for your platform. Everything else is calling cli commands or scripts from pipelines, written in YAML.
Invariably, ppl will write inline scripts instead of actual scripts in their own files. There are also some SDKs for most of these operations that would let you do it in code but they are not always 100% the same as the CLI, some options are different, etc.
Yes, this is how Gitlab pipelines work. It's actually easier to just inline the script most of the time than have a bucket of misc scripts lying around. Especially since you have hooks like before/after_script which would be really awkward to externalize.
