alt Hacker NewsUnless we're talking about figma-like web apps, Content is usually a different department than development.
I know it's becoming more and more outdated nowadays, but if a magazine or a news website is still written by humans rather than AI they need a way to provide formatted text and media, and preview the output.
On the other hand I should add that i've also seen an upward growth in CMSes like WordPress being used exclusively as Online Editors, with content ultimately being exported trough REST to completely different backends and frontends, like a Firebase/NextJS infra.
I'd argue that content written by non-humans makes this even more important. You still likely have a need for a publishing / review workflow & attribution and a way to ensure standards are enforced and not just left to the end-user's own judgement.
Separating delivery from content management also reinforces this. Set up a governed content / user workflow and then let an agent focus on just the presentation after pulling in the content. I'd say this extends well beyond rest as well. A user interacting with something like a voice assistant in an agent might actually be using many interfaces at once (mcp from the assistant, HTML in a card, WebMCP alongside the HTML, browser open on another device for the human.) When that happens you want one canoninical system for the content.