Why are simplex UHF signals rarely heard beyond their radio horizon?

Ultra High Frequency (UHF) signals travel primarily via line-of-sight propagation. Because they travel in a straight line, once they reach the visual or radio horizon, the curvature of the Earth prevents them from being heard further away on the ground. Unlike lower frequency bands, UHF signals have so much energy that they simply punch straight through the Earth's ionosphere and travel out into deep space. They are generally not bent (refracted) back to Earth by the ionosphere, which means they cannot rely on 'skip' to achieve over-the-horizon communication. While the D layer of the ionosphere does absorb some radio waves, this primarily affects lower frequency signals during the daytime, not UHF. Additionally, the FCC regulates power and frequencies, but cannot regulate the physical laws of radio wave distance, making that option a distractor.