Here's why:

* Stars are powered by nuclear fusion. This is a process where lighter atomic nuclei combine to form heavier nuclei, releasing immense amounts of energy.

* The most common element in stars is hydrogen. In the core of stars, the immense pressure and heat force hydrogen nuclei (protons) to fuse together.

* The fusion of two hydrogen nuclei creates a helium nucleus. This is the fundamental process that powers stars.

While helium is the primary product of fusion in stars, further fusion processes can create heavier elements like carbon, oxygen, and even heavier elements depending on the star's mass and stage of its life.