Because the product isn't what's being sold. It's like asking why do Sony and Microsoft make money on selling consoles that cost more to manufacture than they're sold at. You're asking the wrong question.
DC isn't selling the game, he's selling the illusion of being part of the game, of having influence in its development. It's why the more patrons he has, the more they disrupt the development process, they more he gains because the demand for the service increases. You aren't going to bother buying influence on an unimportant project. The more patrons he has, the more "important" the project, the more the desirability to be part of that project, the more patrons. Rinse and repeat. He's also released sufficient to show track record which means patrons feel that they have influence on an important and secure project so they renew their subscriptions.
That's his business model and that's respectable, but let us not pretend he's selling a good, he's not; he's selling a service.
If you don't believe me, ask yourself why he's made the development decisions he's made, the need to rewrite, recode or rewrite aspects of the game, not in downtime while waiting on the art "bottleneck" but as part of each version's development process. Why does he redraw characters, the rigging system is not an adequate answer given his artistic abilities. Is it because suddenly he's a better artist? Well what about in five years time, is he going to be like Sisyphus? Continually improving so there comes a need to redo all artwork and by the time he's finished he's improved again etc. Always pushing that stone up the hill.
And that makes no sense if he's selling a product but makes perfect sense if he's selling the development of the product.