Why wouldn't the developer be on the hook? If Steam doesn't want to be, they're in a powerful position where they can say, "You are liable for chargebacks. If you don't like it, don't sell here."
You either buy it directly to your account, or gift it directly to a friend. Either way, it's locked to an account at the point of purchase.
Steam does allow developers to generate steam keys, which the developers can sell elsewhere (or give away). But then steam isn't handling the payment processing, and whoever is, often developers, is responsible for handling chargebacks.
ie - chargeback occurs and they disable the game for that key?