You forgot to put "in my opinion" in your post. There is apparently a sizable enough fan-base for racing games that the dev companies make enough profit to come out with them again and again.

[quote]What is really interesting is how a racing game can be so much fun?[/quote]Because of taste, that's how.

There is a moment where you are about to win and if you lose you think "I can win that" and do it again and as you progress you get better and better, unlocking new maps and cars and challenges. It's a good formula, if you fail all the time then of course it's boring.