Softer Iron will loose it's edge quicker.

Many ancient weapons and tools were infact steel, Celtic swords had high-carbon edges but I'm not sure they qualified as steel while Iberian blades were in fact more or less steel. Even some Roman Galdii were in fact high-carbon iron on the outside, some examples apparently had coal dust hammered into them.

I'm sure there were smiths who could made decent iron armour but they would have been few and far between and any smith of that level of skill would work in bronze anyway.

Even in the Hellenistic age Bronze was the supperior alloy in general, it just wasn't ecenomical.