The front page of imgur, for me at least, is a grid of images. This grid will expand as you scroll down, but for all intents and purposes those are second, third, and further pages. There is a 14x4 grid for the front page, which consists of the 56 'most viral' images. To earn a spot within this top 56 most viral images, an image has to be considered 'more viral' than all but at least 55 other images. Since Reddit is the king of viral, it constantly floods images which increases the 'virality' of said images. Since this image does not have that support from Reddit, it is nearly impossible for this image to become one of the top 56 most viral images. I don't see what's hard to understand about that.