I mean, it's pretty obvious that such agreement on the part of the funders increases the likelihood that they will lose their money. So why agree?

I guess the person shipping the product could hope that the funders aren't assholes or theives and actually will agree that the product was shipped when it ships, but isn't the smart contract supposed to make such human signs of good will unnecessary? Otherwise, why have a smart contract (or any contract, really), as you can just rely on the good will of the participants?