Ruby On Rails is well known for not being at the fast end of the spectrum, so it needs lots of machines, and lots of machines gives reason to user Kubernetes.
A NewsDesk application written in something compiled for example golang would be much faster and likely could run on a single server.
The benefit of single server being you don't need kubernetes and can spend that development resource on developing application features.
In theory, from a performance point of view, we could easily run our main Rails monolith on a single server.
One does not chose single server deployments when reaching for four nines of uptime though. We also run a lot of ancillary applications / staging environments etc which is what warrants a cohesive deployment platform.
No doubt with Github, AirBnB, Shopify and other big sites RoR is bigger for the front end.
But now if lots of those sites are running on K8s with Argo CD or something or on a cloud platform where the infrastructure is provisioned with Terraform Go is supporting a great deal of things but it's far less visible.
