Here's why:

* Kuiper Belt: This is a region beyond Neptune, populated by icy bodies. Comets originating from the Kuiper Belt have relatively short orbital periods, ranging from a few years to a few hundred years.

* Oort Cloud: This is a much more distant spherical cloud of icy objects surrounding the solar system. Comets from the Oort Cloud have much longer orbital periods, often thousands or millions of years.

So, while both the Kuiper Belt and Oort Cloud contribute to comets, short-period comets primarily come from the Kuiper Belt.