There's a few answers to that question, but one you should read is from General Hugh Shelton, Chairman of the Joint Chiefs during President Clinton's tenure:
...Both times that Secretary Cohen and I made our pleas, Secretary of State Albright pushed back and said no, the Taliban constitutes a legitimate sovereign government and we need to respect that—we need to demarche them first and give them a chance to correct their ways.
I don’t care what logo is embossed on the letterhead, as far as I’m concerned a demarche is basically a letter of reprimand, a slap on the wrist telling them that we believe you are supporting terrorism and we are not going to put up with it any longer...
There's more here at Command Posts.
Shelton's memoir Without Hesitation: The Odyssey of an American Warrior (with Ron Levinson and Malcolm McConnell) chronicles the general's incredible journey from a small farming community in North Carolina to the highest level of American military and political power at the Pentagon and White House.