Here's why:

* Eukaryotic Cells: These cells have a nucleus and other membrane-bound organelles, which are necessary for the complex processes involved in multicellularity. Prokaryotic cells, which lack these features, are not thought to be the direct ancestors of multicellular life.

* Coloniality: The first step in the evolution of multicellularity likely involved the formation of colonies, where individual cells stuck together. These colonies could have benefited from increased size and specialization.

* Specialization: Over time, cells within these colonies began to specialize, taking on different roles and contributing to the overall function of the organism. This specialization is a key feature of multicellularity.

While the exact process of this evolution is still being researched, it's clear that eukaryotic cells provided the necessary complexity for multicellular life to arise.