I understand what you are saying, SGA provide time saving resource to be used in your game, you do not have to use it as your main source of game art.
However it can be helpful to have game resources to work from, or just use it in game where you see fit. You can pay artist to do the work specifically for your game that, but sometimes it is more effective to use assets that already been done, there are some resources that doesn't need to be done again and again, for example, trees, potion icons, rocks etc.