As I recall, this show ended in 2001, soon after the disaster of 9/11. In my view, the writers may have taken that opportunity to cancel the show due to world events. How would the writers handle a situation like 9/11 in the show? Do they ignore it? Do they attempt a back step and show a means to prevent the tragedy? If so, how could that have been done in a tasteful manner as to not offend the thousands of Americans killed on that day?
I don't know anything about the actors getting along or not getting along, or about the ratings of the show at that time, but if there were problems on the set, the time seemed perfect to end the show with some 'dignity'.