Traction looks to be a limitation.

I think the lines are taken that way because the cars are too powerful to use a realistic racing line so they take the quickest turn possible and straighten out the cars before accelerating.

Of course these drivers are very good and agile, but I wonder also if very particular lines are too hard to adhere to/too hard to accurately reproduce every lap. It seems plausible that steering isn't as precise as it could be, constant change of perspective from the view point makes it hard to assess entry and exit points, and that the steering feedback isn't what it needs to be to allow for actual racing lines.