Many sites use JavaScript client-rendering, even for static content. Sometimes, the analytics failure blocks the rendering. I've experimented it recently, with a blank page for a French governmental site (securite routiere) and with a truncated content for an American newspaper (Boston Globe, IIRC).
When you send a server-rendered page, you know the content is present, and very probably it renders correctly on the client. Transmission errors are logged by the web server. With a SPA, many factors could break the rendering, and the web server won't hear about it unless hard work is done to collect JS errors.