If this is a valid argument why?

Because I went out and bought the presents under the tree. I put the money under the pillow. Just because dinosaurs are not around do not mean they never existed. There was a Santa Claus. He is dead but his work continues. Just as why do we still have radios Marconi is dead. No one said leprechauns exist but there are little people and they take offense to be referred to in this way. The last one is in your imagination I can not help you there.