most support volume comes through voice, and you need a layer to interpret what the customer intent is
additionally for many use cases it's not feasible from an eng standpoint to expose a separate api for each entire workflow, instead they typically have many smaller composable steps that need to be strung together in a certain order depending on the situation
There's no reason the app itself couldn't string together those composable steps into an action performed when the user invokes it. OP's point is there is that neither an LLM or a voice layer is really required, unless you're deliberately aiming to frustrate the user by adding extra steps (chat, phone call). Customer intent can be determined with good UX.
additionally for many use cases it's not feasible from an eng standpoint to expose a separate api for each entire workflow, instead they typically have many smaller composable steps that need to be strung together in a certain order depending on the situation
its well fit for an llm + tools