Here's why:

* Interneurons make up the vast majority of neurons in the central nervous system (CNS). They act as connectors between other neurons, enabling communication within the brain and spinal cord.

* Sensory neurons carry signals from the body to the CNS, and motor neurons carry signals from the CNS to muscles and glands. While essential, they are fewer in number compared to interneurons.

Therefore, while all three neuron types are crucial for the nervous system's function, interneurons are the most numerous.