Right, but validation logic and state transferred by the server isn't in-memory state. The fact that the pages completely reload on each request clears a lot of cruft that doesn't get cleared on pages whose lifetime is tens or hundreds of views.
Every SPA I come across, especially when using React, uses persistent state so that in-memory changes are synced to cookie/localStorage/server so they survive refreshes. Every popular state management library even supports this natively. And all of that state combined still requires less memory than any of the images loaded, or the JS bundles themselves.
Every SPA I come across, especially when using React, uses persistent state so that in-memory changes are synced to cookie/localStorage/server so they survive refreshes. Every popular state management library even supports this natively. And all of that state combined still requires less memory than any of the images loaded, or the JS bundles themselves.