There is no answer to migration, education and communication raises expectations and ambitions which young people cannot realize I their home country. Add to that population growth and civil unrest all through the developing world, just one family member with a good job could be supporting lots of others.
It’s not just traffickers encouraging migrants, probably a majority have family or friends living in the U.K. that encourage relatives to join them. They are the lucky ones they will work for and marry into the community and their children will be British. The unlucky ones with no contacts would be doing bonded labour, virtual slavery to pay for their transport, some would be allowed to send money home, some are never heard of again disappearing into the underworld.
This summer I met a young woman mid 20s from Africa who admitted to being trafficked and was on holiday with her German boyfriend, she lived in Frankfurt and worked in a care home. I guess she is fairly typical well educated, with the prospect of marriage and 6 children, a life of drudgery in a dusty village, decided to take the risk and was lucky.