Why don't soccer player become freelance professionals rather than?
A couple of reasons, the first of which is the reason why anyone would prefer a long-term contract to freelance worknamely, stability. Having a contract obligates your employer to pay you a consistent, regular salary for an agreed-upon time, which is appealing to anyone who has regular expenses they need to take care of. One of the major drawbacks to freelance work is that the income it produces can be irregular and unpredictable. The second reason applies more specifically to sports. Most professional sports leagues in the world have restrictions in place on when and how players can move from team to team. Greg Gordon has pretty effectively explained why this is. Without such restrictions, there would be no constancy within teams, no reason for fans to bond with players or form allegiances, and competitions would become meaningless exercises since the same players would never be involved from match to match. What would it mean for Chelsea to win the Premier League (for example) if Chelsea had been shuffling players with their opponents all season long? Matches would be won by whoever has the cash on-hand to hire Leo Messi this week. Why would I become, say, a Liverpool fan, if Liverpool were a different team every week? Sports organizations have determined from experience that this model is not tenable. (Transfer restrictions didn't always exist, and the early professional days of the sport in the early 1900s were an absolute mess for these reasons.) Transfer restrictions ensure that players receive regular salaries (pretty much the opposite of slavery), and ensure that fans continue to form emotional bonds with players, which is essential to the economic health of the sport.