Thanks for asking, i am Vietnamese living in the UK for about 5 years now, so i think i am qualified to answer the question. But are you talking about 39 people who died? If this is the case, then the answer is as below
We cannot blame the country, we have to blame the consequence of the Vietnam war which left behind the poverty after half a century. Even though its economy is reported to develop rapidly, there still too many people who does not have a proper job living in the countryside with low education. They consider living in a developed country like the USA and Western countries as in heaven.
Let me put this in this way, the minimum wage per month in Vietnam is about 130 GBP (even lower) and they have to work all day every day. In the UK, it's the wage of 2 days of a nails technician (major job for most overseas Vietnamese), or even 1 day. They will send money back home, to their family, to support their beloved one. As far as i can see, they work very hard when they are in the UK. There are British beggars, but there is no Vietnamese beggar in the UK.
What is so bad about Vietnam that makes people want to leave?
Well, that said, they do not earn enough, so they are willing to take the risk.
You may also ask why they want to take the risk. A short answer is: to seek the opportunity to permanently and legally stay in the UK
Wait! What? Legally?
Yes!!!
There are a few steps in order for them to stay in the UK. (Disclaimer: this is based on my limited understandings about the circumstances)
First, work to earn money, doing nails or planting weeds, etc. to pay the lawyers
Get caught by the police.
Tell the police that they are victim of trafficking (Regardless the truth or not). They will be killed if they are sent back to VN (again, regardless the truth, it can be true or not, i don’t know)
The lawyers will help them out
if they win, they will stay, if not they will be sent back to VN
above is a simplified version of the story, each person Will have a different story.
hope that this makes sense