I've kinda seen this whole idea in comments for the new Lotus in iRacing, people saying it will be around for a week, and then the server numbers will drop as people get over the novelty and go back to driving the things they love.
Seems in most cases, what they love is what drivers can easily get on with and drive well-ish.
I always see Durge's server there, sometimes with quite a few in it. But I have no interest in running around in F3's all the time. But then, I remember Durge ran a one off 60's F1 server at Brianza, sweeeeeet, I'm in. But then that was a bit too much for a few of the drivers, and a couple of laps in the race after so many had wrecked, I remember Durge saying something along the lines of "Right, time to go back to the F3's" XD
If the majority of people can't drive the hard cars well and get frustrated, for the most part, the are not going to be enjoying it. It makes perfect sense then, noone wants to spend their down time/gaming time ****ting round at the back of the field struggling with a stupidly hard car, while they could be having a fun race in a Clio with a bunch of others.
Which leaves us with leagues, which is fine XD