Weapons and armour are supposed to be shiny and well maintained - if they are allowed to rust, they might become less effective at the slicing and dicing.
Although wouldn't it be cool if we could find some ancient weapon or armour set in an ancient tomb somewhere, and then use the yet-to-be-implemented crafting system to restore it to its shiny glory?
Oh geez that reminds me to go do some armour and bow maintenance in real life (I play SCA and my gear hasn't seen much use over the past year due to COVID lack of war events)
Well, I would say real weapons are dull and slightly greasy. Most metal isn't electroplated that you would use for actual combat. The real stuff, steel which is Carbon and Iron - needs to be kept oiled and maintained.
This is of course leaving out the magic weapons which of course look all kinds of pretty and much better quality with gold accents and nice wood handles and flourishes.
But back to the original point I think they do a pretty good job of showcasing standard weapons that are non-masterwork with some notches and bits of twine holding the pommel to the blade..etc.
There is a single "Scrap Sword" in the game that drops off the Gnoll Fangs that is a rusty mess, looks like a possible longsword and does 1d6
https://baldursgate3.wiki.fextralife.com/Scrap+Sword