I think you are confused. The quotas (which are EU-wide) are there to protect farmers. By limiting the production there is no surplus (there used to be extraordinary surpluses) and therefore the prices are guaranteed not to drop or fluctuate too much. This also prevents monopolies from dominating the market. Particularly benefited are Italians, who would have a hard time competing against milk powerhouses in Germany.

As for cars, they are decidedly different products than food.