Valve has become one of the biggest companies in gaming, their Steam service being the dominate platform for PC enthusiasts. They've created some of the most universally acclaimed franchises, including the fan-favorite Half-Life series, which ended with “Episode Two” in 2007. Since then, fans have asked time and time again for Valve to continue the franchise, but to no avail. In an interview with The Washington Post, which was conducted last Friday, Gabe Newell gave his reasons as to why Half-Life 3 hasn't become a reality, namely due to the company's decision to focus on multiplayer content.
Being really good at Half-Life level design is not as nearly as valued as thinking of how to design social multiplayer experiences...The key is just to continue to follow where the customers are leading.
So far, games like Dota 2 and Team Fortress 2 have become incredibly successful for the company and are still played by a large audience. The multiplayer aspect of Valve's Portal 2 also took center stage following the game's single player campaign, with several pieces of follow-up DLC having been released. Of course, that isn't to say that there aren't thousands of people clamoring for another entry in the Half-Life series. Valve most likely realizes that another Half-Life wouldn't have the lasting affect of games like Team Fortress 2, which can be constantly updated with new content for players to enjoy together. With all of this said, Newell certainly didn't rule out the possibility of a future Half-Life 3, though we probably shouldn't expect to see it any time in the near future.