I like to think the machines actually were using them for processing power, and the humans themselves just misunderstood (or oversimplified for Neo) what was actually going on.
My first favorite would have been: they don’t use the humans for anything, the pods are just the most efficient way to store humans. The machines think they are being benevolent, just want peace and quiet and for humans to stop doing dramatic things like scorching the sky. But I don’t know where the plot would go from there.