Perhaps the SPA pattern, for all the justifications from developers (and yes, of course there are genuine cases where it's a good fit) is really an outcome of Conway's Law[1] in action. In a large enough organization, you corral your dev teams into isolated, specialist "backend" and "frontend" groups which end up communicating largely through decoupled APIs. As with microservices, it's not really about whether this is the most efficient and user-friendly approach to delivering useful apps to the end users, but how much this architecture mirrors your company's org chart.

[1] https://en.wikipedia.org/wiki/Conway's_law