Here's why:

* Nuclear fission is the process of splitting atoms, releasing energy in the form of heat. This is the basis of nuclear power plants, which are currently used around the world to generate electricity.

* Nuclear fusion, while promising for the future, is still in the research and development stage. It involves fusing atoms together, releasing even more energy than fission. However, achieving sustained fusion reactions on a large scale has proven to be extremely challenging.

So, while fusion holds immense potential, fission is the only nuclear process currently being used to generate electricity on a commercial scale.