Rob Crilly at the Telegraph tries to answer this question. I think that the answer is best summed up on the movie, Independence Day, where the alien pilot is asked what the aliens want. Its reply: "We want you to die."
Actually, there are some pragmatic reasons for the Taliban not to talk. The U.S. and NATO have announced pull out dates, so they can simply wait us out. Also, they have become narco-terrorists, so they benefit from the chaos that allows them to pursue the opium trade. Finally, if there is peace, what are they to do? They are fighters, not citizens.
From the perspective of Western nations, the only really successful wars against insurgencies have been the wars against the American Indians and the Second Boer War. However, if we are not willing to engage in similar strategies, we will lose. Thus, unless we are willing to engage in such strategies, we shouldn't become involved.