Exactly. This is what system-ui should be but some browsers instead default to something else, perhaps in a misguided effort to make their UA look consistent between platforms, to many use a font-list like the above to try enforce what system-ui should be. Unfortunately it falls apart if the user has fonts for other systems installed (perhaps for compatibility with others they collaborate with on documents, or to be able to view HTML more exactly as those users will see it) and those users get someone else's system font instead because it is ahead of thiers in the list.