Backbone.js is a great example of an abstraction pushed too far. While we initially liked the ease of wire-up, in practice it suffers from the same issues as all such databound frameworks from WebForms to client/server tools. We find that it blurs the framework and model too much, forcing either bad architectural decisions or elaborate framework hackery in order to preserve sanity.
As the industry shifted from desktop GUI development to the web, it seemed natural to port the most successful patterns and designs to the new paradigm. After 15 years of trying, we feel that there are still no component-based frameworks that have successfully achieved this. We recommend not attempting to make web development into something that it fundamentally is not. It is time to accept the page and request-based nature of the web, and focus on the frameworks that support - rather than work against - these concepts.
This seems reasonable, but single page apps don't have a page and request-based nature, and Backbone seems a good fit for this case.