Imagine you run the support forums for a popular product, e.g. a web browser.
Several hundred million people use your product every day.
Whenever they visit your forum, it's because they either have:
1) A really basic problem they want solved.
2) A really advanced problem they want solved.
3) To complain about something you can't solve.
You can't build a community from this audience. This audience doesn't have enough in common. The goal for participants is to find responses to questions as quickly as possible. The game is to make this process as efficient as possible.
Compare with with FitBit, another community for an audience which will may eventually millions of members. This audience has a lot in common. They have a common goal and purpose. You can build a community among this group.
Generally, if the product isn't very expensive, something we spend a lot of time consciously using, emotionally provocative, or representative of our identity, it's going to be very difficult to build a genuine community around it. So don't try.
Only build a community when the audience has a strong common interest.
This sounds really obvious, and it is, but we still see too many organizations trying to force a community when it's not possible.