As for the decreasing numbers it is too long to maintain interest. One week per round would be plenty.
I think it was 1 week per round last year so there's probably some truth to that.
Not for me though. I wish it were still going and am bummed it's over.
I could time trial like that all day, every day.
I think another possible reason for the low numbers is because it wasn't a separate PSN download/install like it's been in years past. If you didn't have GT6, you couldn't play.