Why? Because studies have shown that these furry beasties cause the average human being to smile 98.67% of the time when they are viewing them on the web.*
That number increases dramatically when they do something "bad" and skyrockets when viewing kittens.**
So here you go. You are welcome.
*This estimation is factually correct only in the spirit of I think it is - I made it up - Dave Barry does it all the time.
** This is also an estimation based on the Dave Barry School of guaranteed estimates.