Community building can be done without any coding, coding can be done without any community. However, to build a large project you need them both.
In a large volunteer project like this, not everything can be worked on. You become selective. We are going to major on this thing, or specifically talk about that project to get community engagement and get the thing done. This drives the project, she helps it to stop chasing hairs. Someone has to decide what feature is going in this release to make it ready to be a release candidate.
That group of people, ultimately making and influencing those decisions, is the CoC.
Let's take a for-instance: Sign up boxes.
For years, Linux sign up allows you to record random data into your profile, office, phone number, etc. These are text, and can be anything. Now, what if there's a rising need to add a minicom number(minix, used to be used by the deaf to send messages to an organisation, before email). As a hearing person, this is going to be a low priority for me, so I work on something else. I've got spare capacity, so if the project leaders are calling for help on this thing, I can go and help.
This, ultimately, builds a better over-all product, but it's not something I'd have noticed by myself, because I'm not part of the deaf community.
In our example with NixOS, asking for someone from the community to be a representative on it is not about code quality, but about the issue of visibility. Is there some need that that section of the community needs? Is there a way that the community can do y thing to make the os as a whole more accessible? I don't know the answer, because I'm not a member of that community, just as I'm not a member of the deaf community.
In this case, the merit, the qualification, for being on the CoC is being a member of a section of the community. It brings valuable a viewpoint, and adds a voice at the table that can make a real difference. Most coders know that having a wish list of features at the start can make it infinitely easier to add them, than having to go back an rewrite to make them happen. Having a voice that might need that feature makes a difference
The debate for CoC is about merit, but merit isn't just stubbornly focused on a single talent, it can also be about life experience.