Interesting. I'd always heard it was due to right to work, but after researching it a little bit more it's just how non-competes are handled in my state (South Carolina).

http://www.scnoncompetelawyer.com/

"A covenant not to compete will be upheld only if it is:

(1) necessary for the protection of the legitimate interest of the employer;

(2) reasonably limited in its operation with respect to time and place;

(3) not unduly harsh and oppressive in curtailing the legitimate efforts of the employee to earn a livelihood;

(4) reasonable from the standpoint of sound public policy; and

(5) supported by a valuable consideration.

* * * *

If a covenant not to compete is defective in one of the above referenced areas, it is totally defective and cannot be saved."