Probably because at some stage it's been through HDV 1440x1080, aiming at a 1.33:1 aspect ratio, and not quite getting there. There are a variety of versions of this test card, and it's been through several stages of construction - it's not the original, just a link to show the picture. The full 1920x1080 version has a red x through it to show the centre of the screen.
The original version is available
hereFor more info on the re-scan of the picture for the widescreen (and later hi-def) versions, have a look
here