Discourse in general loads a lot faster than traditional bbs when you click links or try to view a specific post. So what's being gained is better user experie

Discourse in general loads a lot faster than traditional bbs when you click links or try to view a specific post. So what's being gained is better user experience. I'm not sure I see the relevance of the underlying data structure... isn't email just a collection of documents too? Why is gmail a SPA?