Ah, you're right. Though while it doesn't put a hard limit on the number of lawyers, it does limit the number somewhat by the requirement that you have to attend 3 years of an accredited university and then pass the bar exam.

If you know the law but do not have a law degree, you cannot take the bar examination in most states. In California and less than four other states, you can do something like an apprenticeship in order to qualify instead, but (in California) you must be at least 23 to begin. A friend of mine with a solid understanding of the law and a desire to practice law cannot enter the profession because he is not 23 and does not have truckloads of money.