I think there are a couple reasons you don't have much of a record of documentary shooters using Contax G2. First, in the USA, Contax support has always, always, always been terrible. Beyond incompetent, openly abusive.
Secondly, the established shooters were using Leicas 20 years ago, so why change ?
And any new entries into a shrinking area of photography have largely been digital.
Marketing for the Contax has always been to the same folks who drive a Land Cruiser to the golf course. Of course, so too has been Leica in recent years !
But Leica delivers when you need to get of the beaten path, that's what it was designed to do. And being able to pick over 70 years of lenses to suit what you need is a great advantage. I use 2 lenses for portraits, for instance, a new 90 which can see in the dark, seems to be able cut cleanly through any muck in my vision and give me a better image than I deserve to have made. Then there is an old 85 that at 5.6 can show every nick and pore on a face, but not be overt about it. And at f/3.5 or faster, draws everything it sees with clarity and grace, but has no idea that anything out there is wrinkled or unpleasant. And better than an AF SLR, you can put the focus exactly where you want it.