Hardware farmbot

hello … I want to ask about Farmbot. Farmbot consists of Raspberry Pi and Arduino Mega, why not just 1 microcontroller that is using Raspberry Pi without using Arduino Mega. can you explain why you don’t have to use Arduino Mega as a control on a stepper motor. where the raspberry pi can also move the stepper motor … please help. thank you

@ramsyah Simply put, the Arduino provides more GPIO than the Pi has. It also offers better analog pin support.