Business are not getting a perfect match for their job opening, they are getting whoever will work for the price, that is usually someone from eastern europe. I'd really like to see me be disproven. Why a lot end up in the uk can only be because of low taxes, salaries in uk are decades behind NL at least.
I wonder if the mandatory registration in many EU countries isn't also why a lot will choose the UK, it's probably easier to disappear in London when you don't have a job.