The problem is, how do you know those numbers are bias-favored if your sample size is a few dice rolls? And if there is a bias in those few dice rolls, there's no guarantee it will continue. Sure, a more skilled player will always beat a much less skilled player, but the randomness of the dice certainly closes the skill gap.
It's much different than a game like Agricola or Dominion where you're playing 100% against what the other people do and not relying on the outcomes of 4 dice rolls to determine what you want to do on your turn.
The randomness of the board set up partially cancels the bias you introduce into the dice. There are 20 different possible numeric token layouts, and each of those has trillions of different possible tile combinations.
You really have no practical way of knowing in advance which resource tiles will be under the number tokens you have biased for by loading the dice. So cheating in this fashion doesn't really provide that much of an advantage over the other players. Since the intentional cheating is scientifically indistinguishable from randomness, all good players will already be able to compensate for unfavorable variations in die rolls.
It's much different than a game like Agricola or Dominion where you're playing 100% against what the other people do and not relying on the outcomes of 4 dice rolls to determine what you want to do on your turn.