I can't tell whether they're harder or not as I have no comparison, and you might be right that there is no natural affinity between all the diverse groups that I'm trying to attract. But I'd say that at least some of them have quite some affinity/collective identity, e.g. facilitators or the emerging profession of meeting designers. Plus there is something we might call dormant or potential affinity among many people: having studied meetings for 10 years, I have often experienced situations that people have a lot to say about meetings once you raise the issue. The thing is that people don't usually raise the issue. So that's precisely the point with this forum: to provide a space where these conversations can be had. And to create links across existing meetings related affinities.
And I'd say you're wrong about mass base and support.
Mass base: do you know anybody who doesn't participate in any meetings? And even if you don't count all the people who "only" participate and just look at people who organize and/or facilitate/chair meetings, if that's not a mass base, then I don't know what is.
Support: Yes, maybe not in the narrow sense of "here is my product and here is an entire forum to assist you with any questions you may have" but very much so if you think support in terms of "how can I improve this or that aspect of my meetings" or "what do I need to consider when organizing a meeting with Chinese, Australian and German participants?" And I'm completely ignoring examples related to social scientists studying meetings here.
Or maybe I'm misunderstanding what you mean by "affinity" or "the community"?
Anyway, so if I've "nailed my challenges" , then I don't think they can be summarised in those terms...
BTW: how does your mass base argument fit with this: https://www.feverbee.com/appeal/ ?