Answer: population, Portugal and lax EU visa requirements for Brazilians
Brazil has 213million people: that's greater than the combined populations of Britain, Spain, Poland, Portugal, Romania, Hungary and Bulgaria. Brazilians have easy access to work in the EU zone for 90 days out of a given stretch of any 180 day period, and easier still if they have Portuguese, Italian or Spanish dual citizenship, as many do - they are then at liberty without serious time limits. Portugal is the soft underbelly for wider European access- as with Britain, border entry, overstaying and tracking enforcement is poor to non-existent. A 90 day tour with 65 days worked netting £400 earned per day would yield £26k. Brazil's GDP per capita is about £9200 in raw terms. Purchasing power parity (ie life is cheaper in Brazil) makes every £ returned home more valuable yet.
The workforce and incentives are clearly aligned - making the most of the legal window of opportunity would favour spending a relatively small amount of money on promotion to rack-up business in the shortest amount of time (vs the cheaper but unaffordable luxury of reputation-building over the longer term).
If proper enforcement of both trafficking and illegally overstaying & working were rewarded on a per-catch basis, AW would be the lowest hanging fruit imaginable for UK Border Agents.
