I didn't mean trivial in the sense you mean. I mean trivial in that, in comparison to other human interactions, the variables are more limited and therefore lower hanging fruit for automation.
Voice-based systems currently combine all of the limitations of human conversation (e.g., low bandwidth, strongly linear, possibilities hidden) with all the limitations of computers (e.g., not very bright, highly literal, inflexible).
I think the main reason they're so popular for support is that people are bad at accounting. If I install an IVR system, I see that calls to human agents go down, saving me easily measured cash money. But I probably haven't measured the time and cognitive load burden shifted to customers, or the value lost by suboptimal use of whatever they're supporting.