"Needing" is relative. I could make an app making nothing but raw XMLHttpRequest calls, but that only speaks to the capability of talking to a server. In that sense, sure `fetch` is "enough". But from a perspective of a complex application or a complex org, you may want specific properties to be true: for example, you may want that a request to a certain endpoint follows a predetermined schema, or that one can control the granularity of the response data, or maybe you want to abstract over things like streaming, retries or caching to name a few things.

Something that most frameworks struggle with, IMHO, is that they don't consider how coupled network is to the system and when you need to do something like bundle-specific translations in an SSR context, it's very hard to do it in a generic way without touching half a dozen unrelated parts of an app (meaning librarizing concerns that cross-cut across network boundaries is difficult).