It's actually more complicated than that... mk4 ran on a board that was pretty much only used for mk4 and thus nearly everything has to be built from scratch, including one or two processors if I'm not mistaken.
Just because this game is 3d doesn't mean it has anything to do with the other 3d games, which run on playstation hardware (well documented and realitively easy to emulate) as opposed to the custom midway board used only for mk4 and the grid (not so well documented and difficult to emulate).