Obviously I'm not including burnout as the fun in that is trashing opponent cars while you're racing; for myself I enjoyed some of the earlier entries in need for speed (never played the later ones) cause I could crash into other cars and knock them off cliffs and beat them around to give myself an advantage; I just don't know what draws people to say for example Gran Turismo vs.....I don't know, I don't know any other racing games. Other than the 'crashing into other cars' factor, I don't know what the draw to one racing game vs another is.
Ah, I could never get that 'feel' for the difference between racing games; I guess it takes a genuine interest in game genre to truly grasp the important and sometimes subtle differences between subgenres in a game genre.
For myself crashing to give myself an edge was always my favorite part (probably came from the fact that I played the original death rally game (not the remake) and destroying and attacking other cars was awesome); sending cars flying off cliffs or hitting them from behind as we go up a rise in the road to send them flying in NFS2 was awesome, and burnout was just mad fun for that.
There's also I recall like I think a truck racing game that came out ages ago, and lots of motorbike racing games, but I can imagine those most likely play very differently as well (motorbikes for obvious reasons).
Honestly, to the layperson when it comes to what the most realistic racing simulator is, it doesn't really matter. Some real life drivers have complained about iRacing's physics, but at the end of the day, that's where the majority of the competition is, including real life drivers.
To me, there's also a pretty massive difference in various arcade/less realistic games. Daytona USA, Sega Rally and Burnout 3 are all going to feel completely different to each other, and all three of those are some of my all time favorite games. It just depends of whether the focus is on wrecking other cars, racing other cars or trying to get through a route as fast as possible, all of those are going to feel different and have completely different objectives.