I mean compared to a normal business, sure.. but that kind of traffic requires a somewhat competent backend. Tech cost to run the site wouldn't be massive but either are ad revenues unless you also know what you are doing there. So even a moderate cost can cut into revenues as we aren't talking THAT MUCH revenue.
Costs are comparatively small anymore for hosting a forum, you just hire a decent host and it's all taken care of without any human intervention needed. He's in the high five to low six figures range pretty easily using the known data. If he wasn't already rich he'd still not have to work. I think the napkin calculation Null of KiwiFarms made for people was a bit high, and like you mentioned their SEO is actually pretty shit, but it's still a pretty easily acquired chunk of change. Especially since Cerium literally has to do nothing but make sure it's up.
I don't imagine he's making anything like Lore was for a brief period, but that didn't last long anyway. Then his forum split in half a few years later. Now that it's finally been upgraded I assume GAF doesn't cost anywhere near as much per user to run as it used to. And not just because of the split, it's not a backend kludge anymore. He's probably making some money off it again really.
