When designing a multistory  building, there’s quite a few different options to choose for floor framing systems. Floor framing is more loosely coupled to the rest of the building than other structural elements - it’s often possible to swap out flooring systems while leaving the rest of the building unchanged. There’s some limitations - you can’t use a wood framing system in type I or type II construction for instance. And some systems have more natural synergies than others - if the rest of your building is cast concrete, it probably makes sense for your floor to be concrete too. But generally for a given building, there are at least a few different options for floor framing.
Great article, is there any way to get a excel copy of Span v Cost graph or at least actual raw data?
This is good but you're a little bit off on your span capacity for dimensional lumber because you're using a DL+LL combination that's more aggressive than what Code allows for most residential occupancies. 10 lbs per sq. ft DL and and 40 lbs LL governs houses and non-public areas of multifamily dwellings. Only consequence of this to your data sets is that dimensional lumber wins the cost race by a slightly higher margin. However, I've observed that large scale multifamily design tends to favor wood truss floor systems because of easier installation of mechanical components.