Rewarding Individual Skill

Sorry if the title is a bit clickbait but the simple question I have is why is it more rewarding for players to gang up on another rather then win 1v1s? Simply put why does winning a 2v1 net 450g yet a 1v1 or trade is only 300g. Heck getting a trade and first blood is actually worse for the solo player by 50g. The game may be team based but is it necessary to just lock away gold because someone doesn't get ganks.