Because for the most part, City Rp sucks.
Well, it's got the potentiial to be really good. It's just that most everyone who does know how to host, and hosts a CityRp server, they fail at it. Usually due to being incapable of actually setting it up well. With good buildings/events and what not. They also tend to let people do whatever they want, which leads the Rp's to fail. Plus, there's the use of the Criminal and Policeman jobs. Most Badmins who choose Policeman, will simply jail whoever they want, for no reason. And for a long time. Therefore Badmins who are often found on CityRp servers just ruin it.
Simply put, it takes a reasonably good amount of skill to set up a CityRp server, and have it work really well.
And, whenever it's put up, it's simply everywhere. Loads of people who really aren't 'qualified' for hosting CityRp end up hosting servers with it. Clogging up the Server List with '?????'s CityRp's all over the place. It's just an annoyance, and a disapointment when most people join.