Here's why:

* Germinal centers are specialized structures within the lymph nodes and spleen where B cells undergo rapid proliferation and differentiation into antibody-producing plasma cells and memory B cells.

* The cortex of lymph nodes and spleen surrounds the germinal centers and primarily houses B cells. These B cells are in a more quiescent state compared to those in germinal centers and are responsible for primary immune responses.

While other cell types are present in the cortex, such as T cells, macrophages, and follicular dendritic cells, B cells are the dominant population.