I think the biggest difference is that for immigrants, Germany is seen as country where one can prosper, have a good job and a nice car because of its strong economy while Spain is seen as a paradise where you can live a decent life on government subsidies because of its policies, also the weather and culture.

Edit: I must add that here in Spain we have the "okupa" problem where people occupy unused houses for years sometimes before a judge rules they should be taken out.