Why might nations want to retain or develop an Arsenal of nuclear biology and chemical weapons?

Nations may want to retain or develop an arsenal of nuclear, biological, and chemical weapons for deterrent purposes to dissuade potential adversaries from attacking. Additionally, they may see these weapons as a means to protect their national interests and security in a world where other countries possess such weapons. Lastly, some countries may view these weapons as a way to maintain a position of strength and influence in global politics.