Here's why:
* Invited usually describes the state of being asked or requested to attend something.
* It's more commonly used to describe the person or thing being invited, rather than the invitation itself.
For example:
* Incorrect: "The invited was sent to the guests."
* Correct: "The invitations were sent to the guests."
Instead of using "invited" as an adjective, you could use:
* Invited: "The invited guests arrived at the party."
* Formal: "The event had a formal atmosphere."
* Exclusive: "The party was an exclusive gathering."