Brass was pretty. And by 1500 guns were being made with just decorative features.
I doubt, and that’s an opinion, that brass was used to look pretty. Even military muskets were made to look pretty.
Styles have changed, but there is no other explanation for Fish tail, oar butt, club butts, calfs foot style just don’t make sense from just a practical.
Silver and gold wire accents serve no purpose what so ever. The dragon-sea serpent motif on trade guns started on Dutch sea service muskets. These were added on when a plain washer would do
Iron was seen on many guns dating back to the seventeenth century, popular on some southern guns as brass and silver was also seen on these guns too.
Iron was popular on some plains guns, but brass remained popular on many plains guns, and even well on to breechloaders like the yellow boy.
Barrels where in the white, when blueing would be easier to care for. And browning would become popular in the nineteenth century.
A man who just paid to have an engraved barrel on his rifle gun, the real life Deerslayer, wouldn’t be off put by the cost of iron, and the classic SMR often was needlessly fancy in stock profile.
I do think we try to make an explanation for style.
Colored shirts and ‘fufaraw’ was important sold to tough old mountain men. The bright red shirt was a mark of mule skinners.
I THINK the old frontiersman and the trans frontier folks wanted the same thing that we do today, a gun that’s easy on the eyes