Principally, the main role of electron transport chain is to maintain the electrochemical gradient of hydrogen ions (H+) inside the mitochondrial matrix. This is the last step in aerobic cellular respiration and performs a series of redox reactions. Overall, it allows accumulation of H+ inside the mitchondrial matrix. This increased gradient or accumulation of hydrogen ions (H+) is essential because H+ would accept the electrons producing during the reactions. Without this, the flow of electron will be stopped because of high gradient, and production of ATP will not happen as well.
Indeed ETC helps in production of ATP but that is not the main function of electron transport chain rather it is a function of mitochondria.
