Comment by ndiddy

It may also be due to legacy reasons. Japan was a pioneer in adopting HD TV years before the rest of the world, but early HD cameras and video formats like HDCAM and HDV only recorded 1080i at 1440x1080. If their whole video processing chain is set up for 1440x1080, they’d likely have to replace a lot of equipment to switch over to full 1920x1080i.