If everyone could have more craft/gathering slots it could affect the bottom line–token value.
Mats flooding the market, top crafters around every corner, value of everything goes down. Real money token buyers have less incentive to buy in-game gold. And those who use profs to make in-game gold make less of it, therefore less able to buy the game-time tokens.
It would upset the wow economy, which probably a team of seasoned economists set up to begin with.