It's about video streaming. The challenge with Factorio is that there is always lots of very tiny little changes on the screen from all the tiny boxes and trays

It's about video streaming. The challenge with Factorio is that there is always lots of very tiny little changes on the screen from all the tiny boxes and trays of stuff moving around on belts, which means if you want acceptable video quality, you need a lot of bitrate as the usual h264/h265 compression magic of just encoding differences between frames doesn't work out any more - too much change between frames, you're (effectively) forcing the codec to transmit full frames all the time.