Brian Greene discusses this question in either "The elegant universe" or "The fabric of spacetime". I can't remember it all, but it certainly has to do with the time arrow given by the entropy, that is always increasing.
Because experience happens in the present. As we experience things, they are recorded in the right and left hemispheres of our brains..... some of them anyway. They become available for recall at a later time.
I've read that the experience of time as a flowing from the past to the future, is an illusion. All time is in reality present "simultaneously". This does not mean, however, that everything is destined.