Nobody really wants them, not even their home countries.
Andrew Hammel had an interesting post (can't find now) that explained the probably source of many of them but you need to understand the particular morality of extended-family clan based cultures which is very foreign to modern Europeans to get it.
It was based on the frequency them doing grossly abnormal things (like masturbating in public) and the self-description of a couple of them in interviews - one said he'd always been the 'donkey' in the family so they sent him away
short version: In almost any extended family you're liable to find a young male misfit, constantly in trouble for doing stupid things, he's hard to manage and can't find (or keep) a job and all but impossible to marry off.
why not raise the money to send them to Europe?
worst case scenario - he perishes on the way (in which case you comfort yourself that he died trying to help the family so you can fondly remember him) or does something stupid and gets sent back (in which case you can send him away again)
middle case scenario - he disappears, at least he's out of your hair and can't get the whole family in trouble anymore...
best case scenario - he makes it and the journey knocks some of the stupid out of him and maybe he's even able to establish a beachhead and can send for and bring more of the family over safely
Like I said it's a very different mentality but if you understand the collective worldview that still dominates in a lot of the world it makes a certain sense....