Answer:
Eurasian geography has a set of large rivers in the middle of large plains, and the rivers make the plains fertile by distributing fertilizing sediment when they overflow their shores.
These rivers are: the Tigris, the Euphrates, the Indus, and the Yellow River, and where precisely these rives, along with the Nile in Africa, where the first human civilizations emerged.
Another reason is that Eurasia has many areas with easy access to the sea, because of the many inlets, peninsulas, gulfs, inner seas, and canals that dot the continent.