Because, despite having quite literally written the book on the topic and means of exercising soft power and putting together win-win solutions to problems, the discourse in the US is dominated by people for whom the complex, slow and often invisible application of soft power is anathema. You see it here and you see it on dKos. Speech in terms of violence. Problems must be solved now. Patience is not a virtue. Doing nothing rather than doing something stupid that will not improve the situation is weakness. The myth that violence can solve any problem. And the fact that, for many people, war==profit.