Makes sense. But this is exactly what i was saying: the tooling you're using makes it easy to set environment variables, and doesn't make it easy to add config

Makes sense. But this is exactly what i was saying: the tooling you're using makes it easy to set environment variables, and doesn't make it easy to add config files, so in this case, environment variables are easier to use than config files. But there's no fundamental reason for that to be the case. You could imagine a very nearby parallel universe where Kubernetes config files don't let you set environment variables, but do let you inject files. In this universe, you can see other deployment approaches that make config files easier (Puppet and suchlike). And if you're building something from scratch, you can make the choice.