If Christian added a cache layer on his own server he could easily make the finances work.
But... Thats in nobodies interest - Users end up with stale content, Reddit looses users due to stale content and loses revenue due to Christian extending caching times to save money. Also, Christian will make uncachable requests, like for example voting, hard to do, which again hurts reddit as a platform.
Or they'd do some kind of peer-to-peer caching between clients.