I blame video games. After all if video games had never come to pass there would be no NPCs who's only impact on the game consisted of a single line of dialog thus prompting players to ignore them completely. Of course it was bound to happen some time that players ignore NPCs. They are the PCs after all and if we DMs were really honest with ourselves we'd know that NPCs aren't important in the grand scheme of things. But who really wants to admit that when the PCs brushed off that NPCs who had such a great personality and story potential just so they can get to killing things and taking their stuff?