Thanks for your reply!
When i started the forum, there was (big) demand for it because at that time there were only mailing lists (and even worse: Yahoo groups). So i started this online community with only a bunch of people. We always had some crazy ideas to attract people: putting contests online, organizing weekend trips, attending physical meetings of like minded people with stickers and brochures, mostly paid by ourselves. Now the forum survived Whatsapp/Facebook because we have something to offer: a rich history of topics and FAQ's and the promise that we do not sell personal data nor pictures of members.
But the driving force are the forum moderators: they not only maintain, but also come up with great ideas and initiatives and persuade people they know to stay on the forum and leave good content.
So it is a mixed bag really, and a huge amount of work. But rewarding in the end.