The borders of the Ottoman Empire basically coincided with the borders of Byzantium at the time of its greatest power. Why did they not go beyond Byzantium?
In Byzantium, the Turkish conquerors became the upper class of the former society and did not try to change its order. Outside the borders of Byzantium lived peoples who were not used to submission to the “masters” ~ the Romans. These peoples (Persians, Austrians, Poles, Hungarians) resisted the Turks so stubbornly and skillfully that it was not possible to subdue them for a long time.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.