Here's why:

* Nuclear Fusion: Stars generate energy through a process called nuclear fusion. In this process, hydrogen atoms are fused together under immense pressure and heat to form helium. This fusion releases a tremendous amount of energy, which is what makes stars shine.

* Abundance of Hydrogen: Hydrogen is the most abundant element in the universe. This makes it the primary fuel source for stars, as it's readily available and readily fused.

* Other Fuels: While hydrogen is the primary fuel, stars can also fuse heavier elements like helium, carbon, and oxygen as they evolve and their core temperatures increase. However, these processes are less efficient than hydrogen fusion.

So, in essence, stars are giant furnaces that burn hydrogen to produce light, heat, and other forms of energy.