There are plenty of great frameworks for single-pages applications (Angular, Ember, Backbone, ...) that each offer their own interpretations on how to develop. Take Ember for example (only because I am familiar with it). It provides you with all of the scaffolding and plumbing you need for most SPA requirements. It is opinionated on how to structure and build your application and offers tools and abstractions to do so. I like this as it takes a huge number of decisions out of the process when building a new app so that you can concentrate on being productive.

When building vanilla websites though, you are largely left to develop that structure yourself. These websites need Javascript but aren't entirely powered by Javascript. You can use tools and libraries (Grunt, gulp, bower, SASS, coffeescript, ...) but how you use them is really up to you. When the website gets large enough, these home-made solutions generally get complicated and difficult to maintain. There doesn't seem to be a framework or approach aimed at plain websites that don't want single page functionality.

How are you creating your website frontends?