Simplify the following text for a Grade 3 native English-speaking person.
Original: About a third of all reports of Bigfoot sightings are concentrated in the Pacific Northwest , with most of the remaining reports spread throughout the rest of North America . Some Bigfoot advocates , such as cryptozoologist John Willison Green , have postulated that Bigfoot is a worldwide phenomenon .
Simplified: For this reason , some people do not believe in Bigfoot .