You can’t buy the fourth game of Rockstar Games and Gran Theft Auto, one of the most popular game series of the game world on Steam. At least for now.
The Steam version of the game is unfortunately not available for purchase on Steam. The game’s Steam page is still available, but there is no “Buy” button. But independent expansion Grand Theft Auto: Departments from Liberty City are still available for purchase.
The reason for this is not officially announced, but some games of the GTA series have experienced similar situations several times. The reason he lived was that the music of the game was out of license. Probably soon, the game reverts back to Steam.