In the words of Wikipedia, the scattered disc is "a dynamically active zone created by the outward motion of Neptune 4.5 billion years ago", while the Kuiper Belt is "dynamically stable". On its Scattered disc page, Wikipedia explains that "Although the closest scattered–disc objects approach the Sun at about 30–35 AU, their orbits can extend well beyond 100 AU ... The innermost portion of the scattered disc overlaps with ... the Kuiper belt, but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper."
© Haydn Thompson 2021