Why are China ZJ slurry pumps mostly direct coupled (DC)?

Among the many slurry pump series, why does the ZJ series commonly use direct coupling transmission?

Main reason why ZJ slurry pumps adopt direct coupling
The ZJ slurry pump was developed in the 1980s by the Tangshan Coal Research Institute in China. At the time of its design, it was based on the requirements of domestic electric motors. Therefore, most of its performance parameters were designed to match motor characteristics, particularly aligning with the rated motor speed. As a result, there was no need to change the speed through other transmission methods to achieve the required operating conditions.