Still, the end of Mesopotamian records is abrupt. There's a written record from prehistory until the wars of around 700 BC, where the use of writing drops off but doesn't completely stop. But written records in Akkadian, the education of priests and scribes in Akkadian and Sumerian (itself dead for 2000 years by then as a purely liturgical language) basically stops after the fall of Babylon in 539 BC.
I'd note that writing in antiquity was deeply tied to both administration and to religion. The Persians were Zoroastrians; they do not seem to have oppressed, but state support went to Zoroastrianism and not the traditional Mesopotamian cults (and their scribes and schools). They imposed their own administrative structure on the conquered territories. Persian became the written standard, pretty much overnight. Akkadian seems to have ceased to be spoken within a couple generations among the ruling class, and within a few hundred more years it was not only dead but basically forgotten.