What factors influence the use of iron and steel and tool-making and structure-building materials in modern civilizations?
I would guess: (i) malleability; (ii) ductility; (iii) cost; and (iv) ease of synthesis. I suppose you could add in strength and utility.
I am not sure whether those categories I have listed are the ones for which you are looking. Iron and steel are supremely workable, and are now the premier building material. Our knives, our hammers, our shovels, our precision tools are all made out of steel; edged steel tools can hold an edge, and most of the time the edge can be remade and refined by the end user (think of a chef sharpening his/her knives with an iron).
Another factor we should consider is the ease of synthesis. Iron oxides are remarkably common, and the methods to process this ore into useful steel and alloys have been performed by humans for at least 3000 years. Of course this is not to diminish the skill and technology of iron-makers; it is hard to build a furnace that could smelt iron, even with modern resources.