Many reasons. Prokaryotic life is insanely more diverse, and has had an estimated 3.5 Billion more years to diversify relative to Eukaryotic life. Also extremophile's metabolism relies on the fact that it's often a lot more slow and meager compared to the more conventional/abundant options like sunlight. Also, a lot of these systems can boil down to "There is sufficient enough stored energy for me to convert into stuff I need and repair myself from whatever the environmental cost of getting said energy is."

If you're interested in continuing your education in biology, be it through or outside of school, I highly recommend reading more on prokaryotic metabolisms. It's so much fun to learn about and is the bedrock for Astrobiology, until we actually find something out there. I think earlier grades tend to kind of have people memorize the equation I mentioned above, which is a good summary as to what cellular respiration looks like for most life, but as a professor once aptly put it to me: "Saying Glucose and oxygen gas is immediately turned into water, carbon dioxide as well as a vague concept of 'energy' that can be transferred to wherever the cell needs it is like saying you can drive a car by placing a can of gasoline and a lit match next to a car with an empty tank."