One benefit of greater wheel-lock would be a more direct feel when using a 900°-controller, without decreasing the controller's range.
It's really strange that I have to turn the wheel quite a bit more than in real life, where most cars even have more than 900° of steeringwheel rotation (but probably more wheel lock). On the other hand my car doesn't seem to have lots of wheel lock (parking...) and 900° steeringwheel rotation and still you don't have to turn as much as in the XFG for example. I had to restrict the controller to 540° to make LFS feel closer to real life at least in this respect. Something's fishy...
So basically, if a real life FXO-like car only has 30° wheel-lock, then something can't be quite right in LFS. If it has more, and the FXO has some kind of "restricted race lock" then the wheel most probably wouldn't turn 900° either, because it would make the steering less direct than that of the tame road version.
Well, that doesn't answer the original question, but it implies that the answer is most probably not "because it's like this in reality".
So why is it?
And - while we're already there - why do I have to turn more?
btw: scrabby, it took me a couple of seconds to get your avatar, really.