The problem is that if there's any chance an employer will win, there's a cost that the employee needs to consider. If it's not clear that non competes are going to fail immediately, people are going to get bullied by letigious employers, and less letigious employers will actually benefit from the will-he-won't-he of it too.

Also note that there's a fair bit of legal myths floating around society, so if it's not made clear some people will end up backing out when they would have won.