There's 20 million people living in Beijing though, which allready makes it a transportation and housing nightmare, with prices for rent skyrocketing. If you've been to beijing around Spring Festival, where most people head back to their families, you'll notice that it is almost empty. Like positively razed of people. In a way, yes, controlling such migration is a horrible thing to do, but I couldn't imagine Beijing with another 20 million migrant workers trying to crowd their way through the city, along with the major Spring Festival rush that'd happen.