Forums is fundamentally community based, where everyone is expected to pitch in. While companies are socials, there's not a lot of community going around. There are projects, but the deciders form a very small subset of the involved people.

By the way, for email, the etiquette would be to include the context of the discussion in the invitation for the new person coming in. Or send the archive of the discussion to the person. But for the latter to happen would require a much better email client than what most people are using.