It's no accident. According to Rockstar, the game was removed due to some licensing issues. “Due to some music licensing issues, we’ve had to temporarily remove Vice City PC from digital stores. We’ll make it available again as soon as possible," stated the developer.
The song in question that caused the "licensing issue" was apparently Michael Jackson's "Wanna Be Startin' Something", featured on Vice City's in-game radio station Fever 105. For some reason or another, Sony Music Entertainment blocked the content over copyright issues.
Hopefully, Vice City is restored to Steam rather soon. For those anxious about whether or not this will affect the iOS version, Rockstar's confirmed that the licensing issue won't delay Vice City's release on the App Store.