How come Elsa and Anna don’t know about their kingdom’s traditions?

There are क्रिस्मस trees and decorations in the गढ़, महल even before Olaf sets out to find traditions. The sisters had to have known a thing या two about क्रिस्मस traditions. And why does Olaf try to take all the things he "borrowed" back home. Shouldn't the sisters already have most of these things available to them? They are royalty. Maybe it would be better to give these things to those और in need of them