Well, there often is a reason
For Cherche it's an upgrade of her most used weapon.
For Camilla and Hinoka the weapons work with their faction. (Nohr's cavalier and Hoshido's foot soldiers.)
Soren with his Wind brand that has chill atk and owl tome, Lilina with chill res and death blow refine. Previously they had "silver" tomes.
Felicia that got adaptive damage, she also had silver dagger before.
Raven who got Basilikos, before he had brave axe.
Wow, there were a lot I'd forgotten, thanks for them. Now I know they do change things up sometimes, though they kind of have to for the silver weapons.
Pokemon GO
Fire Emblem Heroes
Fate Grand Order
Dragonball Legends
Dragalia Lost
IV Calc
Heroes