Those reasons aren’t known, so must be assumed. The migrants are typically arriving illegally and don’t want the attention of interviews.

Lastly, I’m 50, and can’t document my memory but typically I would listen to news on something like NPR and they would say that a migrant boat was captured, say, from Greece, and say that there’s extremely high unemployment there. Other reasons given would be natural disasters, outbreaks of violence, lack of food, etc.

Well then, they don’t report because the reason varies from migrant to migrant. Usually there will be a line or two in the report about where and possibly why, but anything past that means they have to interview someone who isn’t in a position to be interviewed.