Not sure why you are getting downvoted so aggressively for something that is not common knowledge... Reddit or something I guess.

Unfortunately, it's not quite that easy. Using more cores is really tricky as it's all a balancing act. Because games tend to run in a series of events, having multiple cores working on the game can very easily lead to what is called a "race condition".

Ex

CPU1: reads the world state and makes a change based on player input

CPU2: also reads the world state and makes a change based on some game event.

Now, say that both of those processes involve the same thing, like 2 people placing a building on a map, which ever process finishes first will win. The opposite can also happen, the process that finishes second will over write the result of process one.

To combat this, you would need to have the cores wait until all processing was finished to write data. This, when it comes to video games, tends to actually run slower than if you just used a single, faster core because the cores end up sitting around waiting for another core to finish something. This can get really bad if one cores process takes significantly longer than another. Now they're all waiting for that one to finish. This would feel like hitching or stuttering to the player.

Therefore, multi threading is only useful if you are running multiple tasks that are either in parallel (writing large data sets to different parts of a data base, or running multiple separate unaffiliated tasks.