I believe that the Akkadians adopted Sumerian culture because it was considered to be more sophisticated and advanced compared to theirs. Sumer was viewed as the place where civilization began. Sumerians had developed a writing system and took part in the development of architecture, sciences, and mathematics. For example, they built walled cities that were characterized by public buildings, unconventional and innovative water systems, and agricultural land. In addition, Sumerians had the cuneiform writing system, which was later adopted and used to develop the Akkadian writing system.
Akkadians moved to the south of Mesopotamia, where they took control over Sumer. As with many invasions throughout history, it is likely that the Akkadians adopted Sumerian culture because it made them more powerful and dominant compared to their neighbors in the region.