Because the person creating the image didn’t take the time to optimize the image. It’s probably just a PNG or a JPEG, which is way overkill for representing a NES frame.
Other commenters have mentioned that the NES has 56 colors and uses tiles to draw the frame. If you took the same approach (maybe embedding a GIF tile in an SVG), you could cut down the size of the modern image significantly.
Because the person creating the image didn’t take the time to optimize the image. It’s probably just a PNG or a JPEG, which is way overkill for representing a NES frame.
Other commenters have mentioned that the NES has 56 colors and uses tiles to draw the frame. If you took the same approach (maybe embedding a GIF tile in an SVG), you could cut down the size of the modern image significantly.