Creating, testing, and updating documentation for command line tools takes a tiny fraction of the time and effort required to do the same for GUI tools. At the same time, the command line across Linux distros is subject to way less variation than all the GUIs across the same. Moreover, the fundamentals of the shell and the syntax of the CLI tools are way more stable over time than a given GUI configurator's layout, so CLI documentation will remain correct and useful longer than GUI documentation. Add to that that for many Google-able tasks, the same task may be relevant to headless servers, and you have another, independent cause for CLI documentation to be created without a GUI counterpart and for it to show up highly in search results.
This means that most documentation for advanced tasks in a volunteer-maintained system where everything actually has configurability via the CLI will tend to cover and emphasize CLI methods.
It is arguably possible to have knowledgeable 'power users' who do not know how to use an operating system's CLI. Longtime Windows users probably fit the bill. But on Linux, nobody who has spent enough time actually reading documentation or following tutorials (and made a reasonable effort to understand them) to become a power user is actually unable to use the CLI. The CLI-averse power user just doesn't exist on Linux due to a bit of a chicken-and-egg issue.
PS: The only system directory tree users should ever 'administer' on Linux by directly manipulating files in it is /etc. The grasp of the CLI needed for this is extremely basic, and there are even nice CUA text editors for the terminal these days. There's no wizardry required to do anything that isn't as destructive or risky as confusing the operating system itself (namely the package manager) about the state of the filesystem.