Because long-term you'll end up with a situation, where your special profitable customers leave for greener pastures (those willing/able to pay higher fees) and

Because long-term you'll end up with a situation, where your special profitable customers leave for greener pastures (those willing/able to pay higher fees) and your base customers can't or won't afford it. Short-term they can make some money raises the prices, until supply-demand equilibrium is reached again. But then you shoot yourself in the foot for the long term.