I don't have to give you a good reason, or any reason at all. It's not me trying to get over here. I am not the keeper of other people's reasons and choices.
They come because they feel that it is the best option for them, for reasons they have and they know and which matter enough to them to risk a lot for the chance of the life they want so badly.
It is likely to be money, health services, safety, security, freedom and the feeling of a future. Or other things. Depending on the individual. I don't know. Ask them.
But I do know that I don't hate or blame the individual for a desire for a better life.
Be a bit rich, as a Briton, the ancestors of whom rampaged through the world, taking over other people's land, oppressing and enslaving them, taking everything of value, taking the land and claiming the natural resources and being a bloody good part of the reason why their countries are in such a state today, if I did.