I don't think it has anything to do with aggression. Because AI cars simply don't have the ability to make a turn properly in a clean driving line. They can slam the brakes right at the apex when you are following just behind. Sometimes they don't even brake at all when coming to a hairpin ramming into you. Agression would not help these disappear. I am doing some races in Silverstone for instance. Starting from the back of the grid, I always watch several AI cars collide each other causing a big wreck in T1. Hillarious.
Well it works for me, heck I can even show you video to back up my claims of good tight ai racing. So you saying it can't happen isn't true. It might be for you, but it's not true of the game.