Why did hittites and others migrate from Central Asia to Mesopotamia

The Hittites were an Indo-European people whose origins can be traced to the cultures from the Caucasus and by 3000 BC, approximately, they moved to the region of Anatolia and Near East. While the main reasons for this migration are unknown, many scholars suppose that, like other cultures that also moved to this region, it was due to the search for pastoral regions. In Anatolia, they imposed their culture over the native cultures of the Hattians and Hurrians and established a new kingdom that eventually would gain power and struggle with other Middle Eastern powers, like Babylonia, for the control of Mesopotamia and Levant for strategic reasons.

I took the quiz, and the correct answer is "They needed more land for growing populations."