All my rides are no steel, soo stinking comfy! My "fun" roadbike is an 84 or 85 Bridgstone that I rebuilt with a modern wheelset. Its a 61cm and is only a bit over 17 pounds. Unless I spent really big money I couldn't better that anyhow!
My commuters are both steel, have a Cargo bike, and an 70's Peugot frame. The Peugot is nice in that it has nice relaxed geometry and clearance for big snow tires.
I've had too many Aluminum frames breakdown or fail to use them as an everyday bike, plus there just so stinking uncomfortable in comparison to steel. Carbon is just too fragile to make a good commuter or townie.
But in answer to your question, Carbon is cheap, and so is Aluminum in compairison to Steel, so bike company's make more money on them.