because official servers require valid Steam authentication.
Naive players see the name in the cracked server browser and think they are on an official server. They are not.
To play on official Rust servers with a cracked or non-official Rust client, specifically when you have Rust: Exclusive, here are the general steps and considerations:
In the past, players used "exclusive" scripts to exploit Steam's Family Sharing feature. However, Facepunch disabled Family Sharing for Rust years ago to combat ban-evaders and pirated accounts.