It's not specifically the daily events, though I agree it may play a part. It is also that some people didn't take the jump to premium racing (they want everything but forget it costs RD actual money), and there are a couple of other factors to consider I won't go into now. But know that it has been noticed, I am in discussion about it and throwing ideas around with staff members. We'll certainly give it a good shot to make it work.
As for your side, early sign ups always help so if you plant to race, don't leave it last minute to sign up. People see a larger grid and they sign up. And tag your friends! Additionally, my inbox is always open for suggestions.