Interjection
why on Earth?
(idiomatic) used to add emphasis to "why" when beginning a question.
Why on Earth are you pouring vinegar in your drink?
Not everybody is absolutely stupid. Why on earth would I be racist, what would I be trying to achieve? Morrissey
I mean, if the relationship can't survive the long term, why on earth would it be worth my time and energy for the short term? Nicholas Sparks
Why in the world are we here? Surely not to live in pain and fear. Why on earth are you there, when you're everywhere-come and get your share. John Lennon
I don't think we should get to the state in this or any other country that if someone has a faith they are regarded as curious. Given that [Blair] had that framework – and it's not for me to question his personal beliefs – then why on earth was he employing folk who so clearly didn't? Alex Salmond
Why on earth should I care whether people read me with their eyes or their ears? Lawrence Block
Why on earth would you buy a car like this if you can't drive a stick? There are dozens of cars--new cars--that have automatic transmission. It'd be a million times easier." Adrian shrugged. "I like the color. It matches my living room. Richelle Mead