I think GT Sport is pretty dead in general now. They've stopped updating the game and 7 is on it's way. I've lost interest months ago and mainly play Assetto Corsa on the PC now.
From what I understood drag racing in Gran Turismo has always been incredibly niche, and Sport was a niche entry into the series, so it's no surprise that the drag community was nowhere near as big in this entry even since 2017.