As twk3 has said, we have examined multiple other options.
One big reason we've chosen to implement with Kubernetes is community adoption. You can now run Kubernetes on AWS, GCP, Azure, IBM cloud, as well as a slew of other platforms both on-premise and as a PaaS. With the expanding ecosystem, our decision has only been further confirmed, as the list of available solutions and providers continues to grow rapidly (https://kubernetes.io/docs/setup/pick-right-solution/)
Another big reason is far simpler: ease of use and configuration. A permanent fixture in our work for Cloud Native GitLab has been that this method must be as easy, if not easier to provide a scalable, resilient, highly-available deployment of GitLab at scale.
We can’t say, “This is our new suggested method. By the way, it’s harder.”
What we have found is that many other solutions require a much larger initial investment of time to understand and configure GitLab as a whole solution, as compared to the combination of Kubernetes with Helm. Helm provides us templating, default value handling, component enable/disable logic, and many other extremely useful features. These allow us to provide our users with a practical, streamlined method of installation and configuration, without the need to spend countless hours reding documentation, deciding on the architecture, and making edits to YAML.