I think there are several good reasons for this, but let's just follow Malcolm Gladwell in cutting to the bottom line:
...I also think it's time that business stood up and joined the immigration debate. I think it has been--with the exception of some high-tech firms--shamefully silent on this, which should be one of its top competitiveness issues. Congress should not be shutting down the borders at a time when we're 10 or 15 years away from some very serious workplace shortages, skilled-labor shortages. We've shut the spigot off, and we're keeping out the very people who would drive our economy 10 years out when our workforce retires en masse.
We talk about these as equity issues, as cost issues, as ideological issues, but more than anything else, they're about competitiveness.