Why did the emergence of multicellularity expand the adaptive capabilities of organisms?

If only because in the process of evolution these unicellular organisms developed sexual reproduction, they could exchange hereditary information, which made the cell the most invulnerable. What can we say about the fact that multicellular organisms exchange hereditary information. And besides, sexual reproduction is extremely rare in unicellular organisms, and the exchange of hereditary information is possible only in this way, therefore, for example, conditions would change dramatically, many unicellular organisms would become extinct, but we would stay, but not up to +60 degrees (we will dry out) …