Performance - For pages that have different content for every user, the best performance will be reached by caching the app code on the client, only loading the data needed to render, and rendering once on the client. Rendering on an aws machine that is weaker than my 15 year old macbook is not a recipe for good performance.

User Experience - Every single user action should have no perceptible latency between the action and the feedback that that the action was received. This can't be done gracefully without javascript. Moreover, SPAs enable a better ux by enabling developers to build complex features that wouldn't be possible on traditional webpage.