But when hired, they become tied to a company in a way that the average worker is not, pushing down wages. If they have a rare skill set the US is missing, it

But when hired, they become tied to a company in a way that the average worker is not, pushing down wages. If they have a rare skill set the US is missing, it is better for both them and the workers they compete with if they are allowed to move over here without being tied to the specific employer, so the employer cannot use that as leverage to push down their compensation, and thus market compensation.