Here's why:
* Adjective: Describes a noun. It tells us something about a person, place, or thing. For example: "The comedian's jokes were outrageous."
* Noun: Names a person, place, or thing. For example: "The comedian told outrageous jokes."
If you want to use "outrageous" as a noun, you could use a phrase like: "The outrageousness of his behavior shocked everyone." Here, "outrageousness" is a noun that refers to the quality of being outrageous.