Final answer:
Geothermal power is less utilized because drilling to the depths where the Earth is hot enough to produce steam is a difficult process, limiting geothermal energy production to regions with geological hotspots.
Step-by-step explanation:
Based on the data provided, the reason why geothermal power is not used more often can be inferred to be option D) Drilling through the Earth to reach areas hot enough to create steam is difficult. Geothermal energy relies on accessing heat from the Earth's internal geologic processes to produce electricity or for heating, typically near tectonic plate boundaries where geological hotspots are present. This energy source is not universally practical due to the rarity of these hotspots and the significant technical and financial challenges associated with drilling to the required depths to extract this energy. As such, geothermal power generation is often limited to specific regions where geological conditions permit, further complicated by the need for specialized technology and the substantial investment it entails.