Your assertion is incorrect. Many populations converted to Islam in the Balkans including Greeks, Albanians, Bosnians, Cypriots, basically all over the Ottoman Empire. The island of Crete was a majority Muslim-Greek population. Greece however, did not recognize it's citizens as "Greek" if they were not Greek Orthodox Christians and would label them as either Latin (Greek catholic) or Turkish (Muslim). Bosnia also converted in large numbers as well as other Slavic groups.
Greeks calling Muslims "Turks" an entirely incorrect attribution. Greek nationalists identify religion with race. Greece to this day does not recognize Albanian as an ethnicity and refer to them as either "Greek" (orthodox) or Turkish (Muslim) ignoring that Albanian is an ethnicity with a super-state language shared by both religions that is neither Greek nor Turkish.
Greece expelled ethnically Greek Muslims to Turkey as part of the racial-nationalism that was common in the early 20th century. Turkey did not do the same. It did not classify Christians as "Greek" recognizing that religion does not supersede language and culture. In the population exchange Greek speaking Christians were sent to Greece from Turkey, however, Greeks sent any non-Christian. Greece's intent was not just to create and ethnically homogenous state based on language but also a religiously homogenous state. This was not practiced in the Ottoman Empire that was a Multi-ethnic state led largely by non-Turks.
There are large numbers of converts to Islam in the ottoman