The real motivation for Sandstorm is, and always has been, making it possible for open source and indie developers to build successful web apps.
In today's popular software-as-a-service model, indie development simply is not viable. People do it anyway, but their software is not accessible to the masses. In order for low-budget software to succeed, and in order for open source to make any sense at all, users must be able to run their own instances of the software, at no cost to the developer. We've always had that on desktop and mobile. When it comes to server-side apps, hosting must be decentralized.