Why was most literature during the rule of the Abbasid Caliphate
based on the Koran?

Explanation:

The Abbasid Caliphate (/əˈbæsɪd/ or /ˈæbəsɪd/ Arabic: اَلْخِلَافَةُ ٱلْعَبَّاسِيَّةُ‎, al-Khilāfah al-ʿAbbāsīyah) was the third caliphate to succeed the Islamic prophet Muhammad. It was founded by a dynasty descended from Muhammad's uncle, Abbas ibn Abdul-Muttalib (566–653 CE), from whom the dynasty takes its name.[2] They ruled as caliphs for most of the caliphate from their capital in Baghdad in modern-day Iraq, after having overthrown the Umayyad Caliphate in the Abbasid Revolution of 750 CE (132 AH). The Abbasid Caliphate first centered its government in Kufa, modern-day Iraq, but in 762 the caliph Al-Mansur founded the city of Baghdad, near the ancient Sasanian capital city of Ctesiphon. The Abbasid period was marked by reliance on Persian bureaucrats (notably the Barmakid family) for governing the territories as well as an increasing inclusion of non-Arab Muslims in the ummah (national community). Persian customs were broadly adopted by the ruling elite, and they began patronage of artists and scholars.[3] Baghdad became a center of science, culture, philosophy and invention in what became known as the Golden Age of Islam.

Despite this initial cooperation, the Abbasids of the late 8th century had alienated both non-Arab mawali (clients)[4] and Iranian bureaucrats.[5] They were forced to cede authority over al-Andalus (Spain) to the Umayyads in 756, Morocco to the Idrisids in 788, Ifriqiya and Southern Italy to the Aghlabids in 800, Khorasan and Transoxiana to the Samanids and Persia to the Saffarids in the 870s, and Egypt to the Isma'ili-Shia caliphate of the Fatimids in 969.

The political power of the caliphs was limited with the rise of the Iranian Buyids and the Seljuq Turks, who captured Baghdad in 945 and 1055, respectively. Although Abbasid leadership over the vast Islamic empire was gradually reduced to a ceremonial religious function in much of the Caliphate, the dynasty retained control over its Mesopotamian domain. The Abbasids' period of cultural fruition and its (reduced) territorial control ended in 1258 with the sack of Baghdad by the Mongols under Hulagu Khan and the execution of Al-Musta'sim. The Abbasid line of rulers, and Muslim culture in general, re-centred themselves in the Mamluk capital of Cairo in 1261. Though lacking in political power (with the brief exception of Caliph Al-Musta'in of Cairo), the dynasty continued to claim religious authority until after the Ottoman conquest of Egypt in 1517.