Why do Mars rovers avoid direct-to-Earth links for large data files?

It demands extremely high power output from batteries needed for operations and survival.

Direct communication between a Mars rover on the surface and Earth presents significant engineering challenges, primarily related to power consumption and antenna size. Sending high volumes of data, such as high-resolution images, over the immense interplanetary distance necessitates an extremely high power output from the rover's limited onboard batteries. These batteries are essential for powering mobility systems, scientific instruments, and maintaining the rover's life support systems. Attempting a direct, high-bandwidth transmission would rapidly deplete these critical resources. The relay system solves this by allowing the rover to use a lower-power, short-range link to a nearby orbiter, thereby conserving energy while achieving higher local data rates.