I don't know why but kids and grown-ups all find skulls cool. Would Rock & Roll have been invented without skull images? What about pirates? Would we remember them if their flag had been lollipops or squirrels? Who figured out that skulls were cool? What makes them cool? There are a lot of questions people can't answer, that's for sure.
But if you need skulls in your daily vision-diet, this website will deliver them, one a day, every day.