Simple - the load on their origin servers is cut down significantly. And GraphCDN made it easy and painless to set up. I don't know of any other options that can do schema-aware caching in this way that is as user-friendly as Stellate.

As an aside - I notice you commenting cynically to almost every thread here. A dose of skepticism is fine and of course we should consider alternatives and technical limitations etc. But your tone and activity comes across more of having a personal vendetta against this company. Very strange.