in my family there has been a simple question being raised for as many years i can remember but there has never been a satisfactory answer yet. "if early muslims had all the science, mathematics, geography, philosophy and all fields of science including hundreds of scientists who laid down the foundations of modern science with their works, what happened 800 years ago that all that science just vanished?" Then years…
Imagine Germany in 1945 losing the war, only having one major library, and the allies burn it down, decimate the population to 10% of the prior count[1], and throw the books down to Rhine River "...in such quantities that the river ran black with the ink from the books"[2].
The Mongols just invaded, pillaged and killed in a mind-less fashion. Middle-east was unlucky cause it was just geographically near them. They also wreaked havoc on China, Korea and Russia. Japan was lucky that storm sank their ships (which were forcibly built by conquered Chinese)
I have not studied al-Ghazali but I think the good'ol war had the major role in this decline and the current state of the middle east.
[0]: https://en.wikipedia.org/wiki/Siege_of_Baghdad_(1258)
[1]: https://en.wikipedia.org/wiki/Destruction_under_the_Mongol_E...
[2]: https://en.wikipedia.org/wiki/House_of_Wisdom#Destruction_by...