cabinets of curiosities

I have greatly admired art that is temporary, that exists for a short time and let let go by the artist, native american sand paintings, time based work, or photographers who take polaroid images of others and give them the person in the image. What is it that happens when we take an image with a polaroid camera, play and take something spontaneous, and give it to the person in the image. Why does our culture value preserving and holding onto the past, setting aside art and putting it on a pedestal, gather objects in cabinets of curiosities? Why is it that the end product means more to us than the process of creating and letting go of what it is we have created. Why do some artists become attached to what they have created and resist selling their work.