Because in the other 49 states just cause to fire someone can be as simple as the employer suddenly decides he doesn't like the way you look.
This is fitting in that Montana is currently the only one of the 50 states which is not "at will" meaning basically that an employer has to have a just cause for firing you. Why haven't any of the remaining 49 gotten on board?
My County is Poor and Remote. Fracking Companies Think They Can Abuse It.