The Middle East and North Africa were conquered by the Muslims and quickly converted to Islam. While there are significant Muslim populations in former Ottoman territories in Europe, Christianity is still more common. Why did they kept their religion after the conquest while Egypt, Syria and Iran didn't?
More can be said, but this by /u/Tarsus1994 is an excellent overview for why the Rumelian territories are majority Christian save for Albania and Bosnia & Herzegovina, which are majority muslim.