Why do immigrants think that coming to a developed country like London and Paris, will get a better life?

People will still have problems financially and emotionally. No country is ever perfect. My neighbour is an immigrant, even though he has a nice house with a mortgage, he's still struggling with life in general.
Added (1). Job opportunities? I don't think so, half of the population here are jobless.
Added (2). Sorry I meant England and France

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