Here's a great article by frequent OV commenter Rice Cubs on his blog: Total Market Freedom.
If you’re a good software engineer or a good web designer, you get to work for Microsoft or Facebook or Twitter or Google or whatever. You have a choice. Maybe you decide to work for a company close by in Chicago. Maybe you decide Chicago sucks (blasphemy!) and you’d rather take a chance in Seattle or Birmingham, Alabama. You have a choice. But the athlete doesn’t have a choice in North American pro leagues, and similarly in Japan.
Americans take great pride in the freedoms they want for themsevles, but when it comes to others, they couldn't care less. If every profession hired its employees the way that professional sports leagues do, it would be viewed as a great injustice. Since it doesn't affect most people, they don't care.