I hope you didn't miss the point that Islam was an integral part of the Ottoman Empire. Hence, basically you can say that for the sake to promote Islam (their brand of Islam, of course...) to places as far as they could reached, they built an empire. And you shouldn't compare their methods of spreading Islam with the methods that most of (if not all of...) the European Powers were using at that time to spread Christianity. Of course they should re-establish the Patriarchate, so that they could derive support form the Christians in their realm (Well, during the Ottoman reign Balkan was still largely Orthodox Christian, even until the end of it...). Process of Islamization doesn't need to be done to rush. In fact, such way was way better than the systematic persecution against the despised beliefs that were done by several European powers at those times...