United managed to keep hold of DDG because of luck and almost unrivalled financial power.
I wouldn't say African players necessarily dream of playing for the Spanish giants, there's a lot of love for the British giants here. But Messi and Cristiano rule here (well, until Salah exploded this season anyway).
The reality is also that if Real Madrid chase after Salah in a concrete way, I believe that there will be severe pressure on him to go from his countrymen. Salah's celebrity is at a ridiculous level here and so many people are obsessed with him here in Egypt. To have an Egyptian player playing for one of the 2 Spanish giants..would be seen as a huge achievement.
God, we had that with the Egyptians with Mido and Ghaly, this is only amplified by having such a good player now.