They ask for your Epic Games login to "inject" the hack. Instead, they steal your account and sell your skins.
The only safe and legal way to get Exotic weapons is to play the game as intended. Here is how you actually get them: Free Fortnite Exotic Hack
Most Exotics are sold by specific NPCs (Non-Player Characters) located around the map. They ask for your Epic Games login to "inject" the hack