Imagination is nothing more than the raw matter of all life experience mixed up into separate elements in your mind.
Some people have trouble mixing up the pieces in meaningful new ways. Those are said to lack imagination. Why? Complacence or cowardice? More likely it is ordinary distraction -- a preoccupation with the concrete pre-assembled world already before them.
Others rejoice in the opportunity to create purple elephants with golden hair and flying cities, the ability to time travel and talking porcupines with doctoral degrees.
Imagination is the mind's joyful sandbox, a spread-out game board.