Here's why:

* Somatic: This refers to any cell in the body that is not a germ cell (sperm or egg). Somatic cells are responsible for forming the tissues and organs of the body.

* Diploid: This means that the nucleus contains two sets of chromosomes. In humans, this means 46 chromosomes (23 pairs).

So, "somatic diploid nucleus" is a bit redundant. Since all somatic cells in an organism are diploid, the term "diploid nucleus" is sufficient to describe the nucleus of a somatic cell.