Also, using an existing engine often means giving up the possibility of having unique features or capabilities. Having the only game with multidimensional quad

Also, using an existing engine often means giving up the possibility of having unique features or capabilities. Having the only game with multidimensional quad-resolution bumpmap tensors (in realtime!) can be a major selling point. Of course, in most cases, you'll get a better overall game by focusing on the art, story, gameplay, etc., but that doesn't always translate to sales.