I guess that the only way to improve the number of drivers is to cooperate with other leagues at the moment. In Italy this year the 2 biggest leagues of GTR 2 decided to unify the champ in only one great league, to do the biggest league ever done in Italy with GTR2, and the result was the registration of 100 drivers, divided in 4 servers. Simply amazing
I was quite unhappy with Mogget's decision to stop organizing champ with P&G on GC, despite of the good turnout every race (20 or more racers per race). That said, Mogget was tired of the "old" v2.1, and that caused the shutdown of the GC forum section of the P&G apart for a couple of topics opened by Geoffers lately in this period to invite some GC users on NoGrip events, that are running on the GC servers if I'm not wrong.
However, as it was for the GTR2 Italian champs in 2010/11, in which the drivers were divided in 2 main different leagues with approximately 150 drivers, even the ROTW P&G champ experienced an half grid compared to the 2010/11 champ, from 42 drivers to 24 this year. We can do nothing about this, except to try to unify more than one site in a bigger thing, or things will stay as they are at the moment.
About the P&G, it's even more complicated, cause if I see the example of the VDA team, only 4-5 people have the v2.1 installed on their pc, instead of 10-12 people in previous years, in which I was able to organize even some fun event from time to time. Watching at the turnout during the last season here, the situation in terms of drivers is not so different.
So, the options is only one. Advertise races in every Simracing website, and see if we reach a larger amount of drivers. I bet we will
Evenmore I guess that when the v3 will be released, it will raise a bit the number of drivers.
I hope the league admins here (Tony & Matt) will try to contact other sites, and sort these things out. Easy to say, but difficult to realize... I know.