Here's why:

* Stars are massive balls of hot gas. They are primarily composed of hydrogen and helium, with trace amounts of other elements.

* Nuclear fusion in stars: The immense pressure and heat at the core of a star cause hydrogen atoms to fuse together to form helium. This process releases tremendous amounts of energy, which is what makes stars shine.

* Hydrogen and helium abundance: Hydrogen and helium are the lightest and most abundant elements in the universe.

Let me know if you have any other questions!