And also in some ventures it might be pretty hard to litigate when everything is done behind closed doors. How would you know if a rival trading firm is using an algorithm influenced by yours or not?
But, maybe to your point, just because it's illegal doesn't mean it's easy to litigate. Much of the legal system is specifically to avoid litigation. Apropos to this discussion, even if a contract isn't enforceable, it only has to be perceived as having teeth to give it value. It's like when a baby elephant is tied to a stake and it grows to an adult still thinking that stake prevents it from leaving. All it takes is for an employee to think a non-compete has merit to keep them in place.