It's not weight, it's because they're proven and reliable. You don't want to risk the success of the mission on unproven hardware. For secondary purposes they

It's not weight, it's because they're proven and reliable. You don't want to risk the success of the mission on unproven hardware. For secondary purposes they have no problem running more modern silicon. E.g. the Ingenuity helicopter, as a last-minute addition (and secondary mission) uses much newer hardware and software: https://spectrum.ieee.org/automaton/aerospace/robotic-exploration/nasa-designed-perseverance-helicopter-rover-fly-autonomously-mars https://spectrum.ieee.org/automaton/aerospace/robotic-explor... > There are some avionics components that are very tough and radiation resistant, but much of the technology is commercial grade. The processor board that we used, for instance, is a Snapdragon 801, which is manufactured by Qualcomm. It’s essentially a cell phone class processor, and the board is very small. But ironically, because it’s relatively modern technology, it’s vastly more powerful than the processors that are flying on the rover.