Here's why:

* DNA is the blueprint of life: It contains the genetic instructions for building and maintaining an organism.

* The nucleus is the control center: It houses the DNA and regulates the cell's activities by controlling which genes are expressed.

While some other organelles like mitochondria and chloroplasts have their own DNA, it's a much smaller amount and is considered "extra-nuclear" DNA. The vast majority of an organism's DNA is located in the nucleus.