because if you do it to brand new cards, the finish is very smooth (non porous) so the fanning pow doesn't have as stickey of a surface to adhere to.
so, what ends up happening when you powder new cards is you get a weird feeling deck for a short while, then all the powder just wears off on your hands and you basically have to re-apply after you break in the deck anyways.
oh yeah that's why to break in a deck i recommend hella pharoah weaves and waterfall bridges because it will wear the finish off very evenly across all the cards. I don't recommend lepauls and springs although a lot of people do. the reason is you really only get a certain number of those out of a deck before the stock is basically all ****** up. conversely, with pharoah weaves and one-handed shuffles, the MORE you do them, the better the deck feels!