There is: superior caching & resource management. Even if your non-SPA perfectly caches resources (impossible with bundling), you are still wasting time on parsing/compiling/executing cached scripts on every page reload, which can take up to a few seconds on smartphones.
In my experience in Latin America with 50-150$ Android phones, very few developers/managers in the "western world" actually care about their SPAs performance and in about 9/10 cases the simple backend rendered sites provide a better experience for me.
edit: Of course there also plenty of devs that add a ton of inperformant js to their backend rendered sites, destroying the experience.
The new page request takes place over Ajax, the server sends the whole page, and only the body gets replaced thus avoiding the need for loading common assets and initializing js.
I'm simplifying but hopefully you get the point.