I think: 1) Like you said, people are buying hope. 2) People cannot fathom this degree of improbability. So, the fact that it's at least possible overrides the near-impossibility of it. 3) There is some aspect of entertainment and social-interaction to it. It's a bit like watching sports. Who you're cheering for is irrelevant, and whoever wins doesn't change your life in any way, but still, we watch it.