A similar reason why US hasn't switched from imperial units, just way bigger.
The current system works, replacing it would be a massive multi-decade long change with a lot of opposition. Cultural pride/arrogance plays a big role. It's not inconceivable to think that the Chinese regime might fall in the process if it tried to pull it off. Given all these, the benefits just don't outweigh the costs/risks, at least in the horizon of the next 100 years.
The current system works, replacing it would be a massive multi-decade long change with a lot of opposition. Cultural pride/arrogance plays a big role. It's not inconceivable to think that the Chinese regime might fall in the process if it tried to pull it off. Given all these, the benefits just don't outweigh the costs/risks, at least in the horizon of the next 100 years.