Your question was interviewed many years ago. Because there are too many names of manufacturers, I won't say it here. I directly summarize as follows:
First of all: I don't want to belittle the quality of domestic ceramic bearings. If some domestic manufacturers still can't meet the standard of very good quality ceramic bearings, then we will use brand bearings. It is very cheap to buy a set of small brand ceramic bearings outside, and the price will be high if it is changed to a brand. Remember: it's expensive.
Secondly, the running friction of ceramic bearings is small, which provides significant advantages in industrial applications running at 20000 rpm. When the ceramic bearing only runs at 300 rpm, the slight improvement in efficiency will make your power output change little, which is obviously not worth the greatly increased cost.
Finally, ceramic bearings run very well without grease (silicon nitride, a structural ceramic material with lubricity). After adding grease, the rolling resistance of ceramic bearings is almost the same as that of steel ball bearings in ABEC 3, 5 and 7 standards, and the viscosity of grease leveled the gap in rolling resistance.
The above are basically cited by several foreign researchers. You can see that friction has a special relationship with cost.