Why didn't Kennedy listen to De Gaulle, and Bush didn't listen to Chirac ?

Vietnam: 58000 young American lives --- Irak: 3000 young American lives --- In 1962, De Gaulle advised Kennedy: "For you, intervention in this region will be an entanglement without end. From the moment that nations have awakened, no foreign authority, whatever it means, has any chance of imposing itself on them. You are going to see this. The ideology that you invoke will not change anything. Even more, the mes will confuse it with your will to exert power. This is why the more you commit yourself there against communism, the more the Communists will appear to be champions of national independence, the more they will receive help and, first of all, that which comes from desperation. I predict to you that you will, step by step, become sucked into a bottomless military and political quagmire despite the losses and expenditure that you may squander." . 40 years after, Chirac told Bush not to go.