You have a car. There is a ball, and there are two goals. GO! Rocket league is a simple concept with a superb excecution.
Game design, as a discipline, currently has a fairly serious roadblock; making games is hard.
I’m not saying that code is hard, though it is. I’m not saying that making good art is hard, though it is. I’m saying that game design requires both code and art to support it, so you need to have knowledge of all three domains.