There are many factors in complexity, but a big one for me is what I have to hold in my head – global state. From any given point, what do I need to understand to know what's actually going on.
For Go, this is actually comparatively little. Between a fairly straightforward language, static binaries, and the focus on ease of distribution, there's not a whole lot outside of a codebase itself to think about.
However for a shell like Bash there's a relatively large amount to consider. You're very exposed to the underlying OS, to libraries and system packages, to various tools, to configurations users may have specified, to things being redefined underneath you. There's a lot of global state to consider for a Bash script.
I suspect it is simpler than Kubernetes, but I don't think it's a clear cut case.