secondly, the robot has a higher expense than human. for highest performance, robot needs a high grade parts and have a high price according to moreover robot need repair periodically. unlike human that they just use their ability to work and they can upgrade their abilities by learning which have a low expense. Many companies choose human because they have a low expense to hire and upgrade.
Also, there are more thing that make robot different from human such as exhaustion,speed,accuracy,etc. Robot never tired it can work as long as it have energy but human can't work all times they need a rest to continue work.