the sad fact is that everybody owns different combos, so often people either did not own the car and/or track even though they would have wanted to participate. I once bought one track just to take part in one event of the last RD oval series only to find out that real life messed up my evening that night and I could not take part after all. Never used the track again, which really is a waste of money.
There are probably a couple of good leagues out there, browse the iRacing league pages. For me, the official open servers are fine atm.