It used to be a LOT easier to end under caution than it is now. The rules have changed multiple times to give them the most opportunities to end under green. But here’s the reason why a caution on the last lap ending it makes sense: during last year’s All-Star Race they did away with it and experimented with being able to line them back up no matter how last second the wreck was. Ryan Blaney was literally ten yards from the checkered flag when the caution came out. He crossed the line literally less than a second after the caution waved, and (understandably) had no clue it even happened and thought he won. He unfastened his window net to celebrate and prepare to exit the car…only to be told he had to restart again. So now you’ve got a car with an undone safety device who has to race more.

Would that exact situation happen every time? Probably not. But you can see how last last moment cautions lead to clusterfucks. There’s gotta be a cutoff somewhere and the last lap is a pretty generous place to put it.