> What’s so much better about it?

It's so trivial to put together any CICD pipeline that it barely registers as a skill you need to develop. All jobs run on containers you control, you specify the scripts you want to run in each job (e.g., npm test), and done. For standard pipelines you don't even bother to set precedence and fan-out/fan-in because if you set your stages as the default stages then that's already done for you.

Also nice, GitLab provides terraform providers for it's CICD infrastructure.

GitHub Actions in comparison is a god-awful mess that has only parallel in Azure YAML Pipelines, another abomination that should be used as a punishment instead of a production system.