How are swords "expensive to produce" and "required much material"? They are basically glorified metal bars, that were sharpened.

And armor not advanced? You know what can stop a metal sword? A sheet of metal (formed into any kind of armor or a shield)

They were not used before because it took some while to get the iron / steel process right (and bronze swords dont really work, bronze is too malleable, you can stab with it - like with a spear - but not slash with it, or it bends)

They were not used afterwards because swords against armor are next to useless, and are just suicide against shot&pike.