In F1 it has to flash with the limiter, and flash when rain tyres are fitted.
In any other F1 catagory in the world, pretty much, it only needs to be on when rain tyres are fitted or the race is declared a wet race (even if you are on slicks).
As we don't have rain it isn't required. When we do have rain it'll be pointless anyway as they don't do much when there is spray