> The fact that China has kept using them, despite a very pragmatic government that wanted to move the language more phonetic, should say something about their utility.
Or just inertia. Norway has had a steady stream of language reforms over the last century aimed at bringing the official written language better into sync with a majority of spoken dialects. This is a result of hundreds of years of Danish rule that ended in 1814, followed by the period of national-romanticism in the period up to the subsequent break from Sweden, that led to a lot of desire to make language etc. more uniquely Norwegian.
As a simple example, we inherited parts of Danish counting.
It used to be in some parts of the country that we'd say "fire og tyve" for 24 - literally "four and twenty". This was changed to "tjuefire" (twentyfour) in the early 1950's. Anyone who has learned Norwegian in school since then has learned the new form in school and been marked down for using the old forms etc.
Despite that, and being born to parents who were in primary school when this had just changed and who learned the new forms, I still regularly use the old form.
I never learned it at school, and I occasionally had teachers complain about it. I don't use it consistently, to make matters worse - it's not a conscious choice to use a more conservative style or anything, it's just habit I picked up mostly from my dad, which is persisting in my spoken language now, when I'm 41, despite having changed in a language reform a couple of decades before I was born.
This is a difference where there's no practical benefit at all to the old form - it's longer, and the new form is more consistent with spoken Norwegian overall -, yet more than half a century later the old form still persists out of habit.
In particular, trying to engineer changes to language tends to take a long time even when there's no resistance to the change.