It's baffling to me why more SSR frameworks, Astro and NextJS namely, can't adopt static pages with dynamic paths like SvelteKit. So for example, if you have a page /todos/[todoId] you can't serve those in your static bundle and NextJS straight-out refuse building your app statically. Whereas with SvelteKit, it builds happily and does this beautiful catch-all mechanism where a default response page, say 404.html in C…
I partly agree with you, but it is a design decision that comes with a drawback. A URL /todos/123 cannot be resolved in a SPA in a hard-reload. I.e. if a user were to bookmark /todos/123 or press reload in the browser, the browser would ultimately ask the underlying HTTP server for that file. As you mentioned, you would need a 404 page configured to fetch that - but that requires a configuration in the HTTP server (nginx etc.). So you are not just a static html+js+css+images deploy, you always will need server support. Another issue is, that 4xx errors in the HTTP spec are treated differently than 2xx: most notably, browsers are NOT allowed to cache any 404 responses, no matter what response header your server sends. This will ultimately mean, those /todo/123 bookmarks/hard-reloads will always trigger a full download of the page, even though it would be in the cache. And again, you would always need support in the web server to overwrite 404 pages. While the current NextJS output can be just deployed to something like github-pages or other webspace solutions.
Now, these are just the limitations I can think of, but there are probably more. And to be fair, why "break" the web this way, if you can just use query params: /todo?id=123. This solves all the quirks of the above solution, and is exactly what any server-side app (without JS) would look like, such as PHP etc.