Steel is heavier than aluminum, but it's stronger and they can use thinner tubes so the final bike weight doesn't have to be heavy at all. Steel may be the oldest bike material but current building methods are far from antiquated; just take a look at what Luna is doing with steel! Steel tends to soak up vibration better than aluminum could be quite nice on a bumpy limestone path.

I have three bikes, one each steel, aluminum, and carbon. All very different bikes with very different uses.