What primary physical factor makes detecting most Kuiper Belt Objects extremely difficult?
Answer
Sunlight is incredibly faint at those vast distances
Due to the immense distances from the Sun, these icy bodies reflect very little sunlight, making them appear extremely dim and hard to detect.

Related Questions
What is the approximate range for the number of officially cataloged Kuiper Belt Objects (KBOs) as of recent tallies?Which astronomical body is responsible for maintaining the official register of small solar system bodies like KBOs?What orbital characteristic defines a Kuiper Belt Object as a Plutino?What range of astronomical units (AU) defines the stable orbital region for Classical KBOs?Which object is cited as the largest known Kuiper Belt Object?What primary physical factor makes detecting most Kuiper Belt Objects extremely difficult?How is the total estimated population of Kuiper Belt Objects larger than 100 kilometers across generally estimated?How are the orbits of Scattered Disk Objects typically characterized?Relative to Earth's mass, what is the estimated total mass of the entire Kuiper Belt?Which next-generation telescope is anticipated to significantly increase the confirmed KBO count soon?What key comparative technique is often used in ground-based surveys to identify newly discovered KBOs?