But that's based on your own system, which may be non-obvious to other developers.

Yes, conventions are like that. You have to read the docs.

[...] this kind of naming convention isn't a native part of CSS.

That's true for naming conventions in general.

Well, this stuff was added for a reason. If you know the rules, the SCSS and markup becomes way easier to navigate. Additionally, there are now many properties which can be automatically verified.

It adds structure which wouldn't be there otherwise.