Because immigration would be a damn sight better for the economy if we weren't shackled to Brussels who are as far from pragmatic as I am from voting Labour. If we must have quarter of a million additional people I'd rather they were all selected under the pragmatic policy of choosing people in professions we actually need like every other country on the planet (Australia comes to mind) rather than a policy designed to promote the completely contrived ideology of Europeanism, which was literally invented to prevent the Germans and French having yet another war. Having control over our immigration would be a much greater economic boost than a mix of tens of thousands of people we need along with hundreds of thousands of unskilled workers. It is massively inefficient to be required to take many workers we don't need for every one we do, and it's an inefficiency that is solely the fault of Brussels.

Also, another good reason to oppose the free movement of people in an area that contains very asymmetrically developed regions is because mass migration and all the problems it entails in both the original and the target country is inevitable. The UK only has 94,058 square miles of territory and nobody in their right mind wants to turn England's green and pleasant land into a hellhole of commie blocks and urbanism. Many people hate urban life, do you believe that every resident of the UK should all have to live surrounded in concrete and pollution because people who might not speak English, Welsh or another British language, might not have any significant cultural similarities but are born east of the Urals and north of the Caucus have a sacred right to life in the UK?

I'd support a free movement zone including the developed Commonwealth (Singapore, Canada, Australia, New Zealand, the Bahamas, Cyprus) and the developed parts of Europe (France, Germany, Norway, the Netherlands, Denmark and so on) but not one that includes poorer countries who's development must come at the expense of developed countries and which as a result causes a larger state, more government interference and higher taxes.