Because, when I'm avoiding work, this is the greatest time-waster ever. If you have, have ever had, or know someone with a cat or cats (the films are only a couple minutes long)...
[edit] Heh, looks like someone was inspired by that video. They went and made an iPad game just for cats: http://www.ipadgameforcats.com/ (free)
[edit-2] Oh okay, that one was released just a few days ago... but apparently something similar has existed since mid-May (at a cost of 99¢): App For Cats (which still wasafterthe Iggy viddy on YouTube)
Rather than starting a new thread, I decided to add the following fruity video gag here for the 'digital' vegetarians among FineTunedMac's visitors, as well as for those who are less feline-inclined...