One of the main benefits of the SPA architecture is that it enables a web app to approach the high bar set by the latest generation of native apps (particularly on touch devices) with respect to transitions between application views.
View transitions in modern native apps feature low latency, direct interactive response to user input, and animations that lend a sense of place and physical realism. Like the best intra-view progressive enhancements, these view-transition features aren’t just bells and whistles; when skillfully applied they improve usability and qualitatively enhance the user experience. “Traditional” web app page transitions feel clunky and outdated in comparison.
Unless and until web standards provide a way for traditionally architected web apps to compete with native UIs, web app developers will be tempted (and in some cases forced) to adopt SPAs to close the gap.