Because the great leader of the Turks Kemal Atatürk (translated as the father of the Turks) decided that the state led by him would be Europeanized. If earlier religious authority influenced the state, there were Sharia courts, there was a state religion, obligatory for all.

Today Turkey is a secular state. The Church is separated from the administration of the country. However, the power is civil, civil courts, representatives of other faiths are equalized in rights with Muslims. Islam itself is a little more liberal than in the same Saudi Arabia. Women have full rights.

Useful links for Istanbul travel