I think you may be missing the concept of ‘hydration’. A server side rendered app will deliver the pre rendered markup so that the client has something to immediately display while the framework continues to bootstrap in the background. It makes for much quicker and more efficient first loads, or ‘time to first paint’. A SSR website will still be a CSR website after hydration completes.
In addition, many web crawlers are unable to execute JavaScript. So for many single page applications, or CSR as you call them, they appear as a blank screen to less sophisticated crawlers because the content is never loaded. This is an catastrophe for things like SEO. SSR fixes this issue by delivering the content without regard to JS execution for the initial load.
There are many scenarios you’d want seo and a csr. Let’s say you want a media player. Tons of interactivity, and lots of content. A landing page isn’t going to cut it.
But that’s the beauty of a framework like nuxt or next - you don’t have to choose. You can have your cake and eat it too so to speak.