The flourishing of Islamic science took place not in Baghdad, but in Central Asia, and it was already in steep decline when al-Ghazali wrote his polemics. The reasons for both the rise and decline of the Central Asian enlightenment are fascinating and complex.

The tl;dr is that these cities (most now ruins) relied on very complicated irrigation systems that required a high degree of technical skill to maintain, and were also quite cosmopolitan places culturally, since they were never Arabized and lay on major trade routes, guaranteeing them exposure to ideas and scholarly texts from India (although interestingly, not so much from China).

Anyway, it's a great book and will put the rise and decline of this period in context for you.