cars are pretty easy things to draw for a computer, so that was handled a long time ago, look at nsf underground (2001), the reflections and lighting looks like garbage but the cars look good, from that point in 20 years we could not evolve too much and racing games are often made to be run on pretty old PC and when you are driving you should not really look at them that much, so less detailed assets and less of them makes sense, makes for higher performance and less work for the designers too. most of the work in race game lately has been on physics engines, so that the games are closer to life when it comes to handling and damage.