You say "free market" but the only reason other states work that way is because the courts enforce non-compete agreements. The state has a monopoly on court judgments, after all. In the same way we can say that the 19th century US didn't "restrict" freedoms, it merely "allowed people to own slaves". I'm not saying the comparison is apt, but it's easy to flip around words and say that "California prevents companies from preventing you from working for competitors" instead of "California does not enforce private non-compete contracts".