Here's why:
* It modifies nouns: "Indigenous" describes a characteristic or quality of something. For example:
* Indigenous people (describes the people)
* Indigenous plants (describes the plants)
* Indigenous culture (describes the culture)
* It doesn't act as a verb or a noun: It doesn't convey an action or represent a person, place, or thing on its own.
In contrast, "indigene" is a noun meaning a native inhabitant of a particular place.