The price controls can't be enforced everywhere, or trade would just move to the black market. They are presumably only enforced on stores that are not politic

The price controls can't be enforced everywhere, or trade would just move to the black market. They are presumably only enforced on stores that are not politically connected, and that are large enough to draw notice. When they are forced to sell below cost, these stores won't stock anything, so the price controls have no positive effect.