I don't see why it would be. You can easily determine what resources a player is likely to have, and what they need, by looking at the fully public board.
I'm not, really; the normal mode is that you offer to buy something and you get it or not. But if you want the information, it's publicly available in high but not perfect fidelity, making tracking hands even less valuable than otherwise.
Player 1: "Hey, Player 2, I'll trade my wheat for your brick."
Player 2: "I don't have a brick."
Player 1 knows that Player 2 got two bricks and a wood 3 turns ago, and he bought a road. So the one card that's left over is a brick.
Player 1: "OK, I play a knight development card, I move the robber to your plot, and I take your card. Lo and behold, it's a brick!"