They would, but the consultancy company would want you to buy them out (it has happened with some of my colleagues), and that's not going to be cheap.
There's also been at least one instance where people left the company and were rehired by their client during the do-not-compete timeout of a year; in practice, a do-not-compete clause cannot be enforced in a court, and given that the client is several orders of magnitude larger in terms of finances than the consultancy company, a legal battle wouldn't pan out the way they want it to.
So the guy took the job and the risk, and he still works there. Probably earns a lot more as well.
>in practice, a do-not-compete clause cannot be enforced in a court
Depends. I've known consulting companies that have absolutely enforced them--though the circumstances have usually been around someone setting up their own shop rather than going to a client.
The broader issue with non-competes is more chilling effect than than actual enforcement. When I was with a small consulting firm we wouldn't touch anyone who had an even vaguely related non-compete. Just wasn't worth the risk or even the effort/cost of getting a lawyer involved.
There's also been at least one instance where people left the company and were rehired by their client during the do-not-compete timeout of a year; in practice, a do-not-compete clause cannot be enforced in a court, and given that the client is several orders of magnitude larger in terms of finances than the consultancy company, a legal battle wouldn't pan out the way they want it to.
So the guy took the job and the risk, and he still works there. Probably earns a lot more as well.