Why is the salary of dry gantry milling high?

Heavy workload. Whitney, an American, created the horizontal milling machine in 18 18. In order to mill the spiral groove of twist drill, American Brown made the first universal milling machine in 1862, which is the prototype of the lifting table milling machine. 1884 or so, the gantry milling machine reappeared; In the 1920s, a semi-automatic milling machine appeared, and the workbench can be automatically switched between "fast forward" and "fast forward" by using a stop. Because of this, its workload has reached 12000 per month.