We're the first rich country when they move to the east (from a Romania/Bulgaria POV) - and Germany is the last of Europe to have a reputation for being financially stable, providing social/healthcare coverage and not being overly racist.
France/Great Britain, in contrast, are not very favorable target countries: France has a strong nationalist/right-wing extremist political movement (Le Pen's Front National), and Great Britain, while rich, is not covered by Schengen agreement and excepted from a lot of EU regulations - so it's both difficult to get into, and stay in.