Perhaps I'm just different or easily pleased, or perhaps I'm just a car enthusiast who is more interested in the driving rather than the gaming, even though I consider myself both a fan of driving and gaming.
I personally find it very hard to get bored of driving, no matter what, where or how. There's a lot of features missing for sure, but as long as there's a variety of cars and tracks, and the physics are somewhat decent, then I won't be bored, I will get years out of GT6, just I have from every single GT game and various PC driving sims.
I don't care if I have to drive to the shops in the rain, I don't care if I have to drive a 2000 mile business trip for work, I just enjoy driving. If you get bored easily by driving, then I would have to question your enthusiasm for cars, or guess that a different type of driving game is for you.
This is not a defence of the GT franchise whatsoever, more on the whole driving aspect and driving games in general, I just don't see why someone would play a driving game if they get bored of driving, that's all. Just me, the car and the road, that's all I need, well, and fuel I guess.