Here's why:

* Function: The nucleolus is the site of ribosome biogenesis. It's where the ribosomal RNA (rRNA) is transcribed and assembled with ribosomal proteins to form the subunits of ribosomes.

* Ribosome's Role: Ribosomes are the protein synthesis machinery of the cell. They translate the genetic code from mRNA into amino acid chains, which then fold into functional proteins.

So, the nucleolus is essentially the "factory" for ribosomes, which are the crucial components for protein synthesis.