The only way trading would work is if lots of people didnt have the old unlocks, such as new people to the game. The problem is them new people can quite easily get on an acheivment server and quickly get all the standard unlocks that way.
If they removed achievment unlocks then trading would have a bit more value, but the majority already have old unlocks anyway.
If they removed achievment unlocks then trading would have a bit more value, but the majority already have old unlocks anyway.