Racing sim games have the advantage of being mostly based in the real world, so the developers already know exactly what to model and how to make it look. The creative process can move much faster because of this. There's no need to spend time on deciding on a track's layout, as it already exists. There's no need to decide where to put the trees, spectators, etc because this is already known. There's no need to design the cars, as the designs are already done. I imagine this saves a lot of time, which means they can get right to the actual 3d modeling part much sooner. In a fantasy RPG (or fantasy anything else, really), the developers often need to build a whole new world up from the ground. They need to decide which plants exist, what they look like, which creatures inhabits the world, how they look and behave. In many cases, they create an entire creation myth for the world and makes the creatures and other organisms of the world tie in to it in certain ways. All this is of course on top of the actual 3d modelling process. In many cases, all this work is done just to make the world of 1-3 games, before they have to start all over again and create entirely new worlds. Not to mention, in these games, you generally move a lot slower than 300 km/h, so the players get a much better look at the environment, making it way easier for them to notice any sub-par texture, weird polygon and whatnot.