Ialyrn:
Most racing series and track rules dictate the the edge of the track is white line to white line. What each individual racing series allows to be used beyond that is up to them, but nearly all of them state in the actual rules that anything outside the lines isnt the racing surface. The drivers get judged on a case by case basis in real world races, and usually only incur a penalty/warning if they gain a lasting advantage that is deemed unfair to other competitors. T10 cant do that with Forza, so it has to be a singlular hard and fast rule for everyone who plays the game. In Forza 7, T10 have made the white line to white line the difinative track edge, which lets be honest here; is far better than the liberties people could take previously. Have people forgotton how badly Monza could be cut in FM6 before the tire walls where added? You could take a very straightened line though most seconds on that track. There is also the fact that T10 clearly want Forza to be taken more seriously within the realm of E-sports. That cant be done with the “anything goes” system that has been in Forza up till now.
If you want the old way back, then at this point in time; your only option is to go back to FM4/5/6 and have at it.
Edit: Also, you may not always see the race drivers gain a penalty during the televised race. But they do happen. If you want to see how often they are incured for leaving the track in F1 for example, then there are resources out there that allow you to see.
2018 F1 penalties index – RaceFans = (9 instances of leaving the track)
2017 F1 penalties index – RaceFans = (11 instances of leaving the track)
2016 F1 penalties index – RaceFans = (14 instances of leaving the track)
2015 F1 penalties index – RaceFans =(20 instances of leaving the track)
Those drivers IRL with penalties are punished if they gained an advantage when going off track.