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Why is the Kuiper belt thought to be the source of most short-period comets?

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Kuiper belt binary object — Kuiper belt An artist's rendition of a binary object in the Kuiper belt. The two objects depicted orbit each other at the edge of the solar system.

The Kuiper belt is considered the primary source of most short-period comets because it provides a flattened reservoir of icy bodies that can be dynamically scattered into the inner solar system.12

While it was previously hypothesized that short-period comets originated from the Oort cloud through planetary perturbations, computer simulations demonstrated that this process was too inefficient to maintain the observed population of comets. In contrast, the Kuiper belt—specifically the scattered disk—contains objects whose orbits are influenced by Neptune. Neptune can gravitationally scatter these bodies inward, where they may transition into Centaur objects and eventually become short-period comets.3241

This origin explains the dynamical characteristics of Jupiter-family comets, which typically have orbits with low inclinations relative to the ecliptic. Such a distribution is consistent with a flattened source like the Kuiper belt, rather than the nearly isotropic distribution of comets arriving from the distant Oort cloud.2