Prefetching is often an element of a pleasant user experience. It also can bring difficult UI problems with it (when is information too stale to display, etc), but that just means it's not easy.

It feels like so many apps are designed by people who never have experienced a bad connection, and just assume that their app can download everything it needs quickly as soon as it starts up. What you end up with is bad experiences when your connection is slow or has high latency.