A common story.
You ask your members what you want, get some good responses, implement those ideas, and the level of activity doesn’t go up.
The problem is the people most likely to respond are also those who are already as active as they’re likely to be. They’re the vocal minority. They’re the small group that already participate in most discussions about the topic.
They’re already getting everything they need to be as active as they can be. You need data from the people who aren’t participating much.
You need the people that make 1 to 5 contributions per month. Build a segment of this group. Send your survey to them. Interview them. Incentivise the responses to this survey. Compare them with the vocal minority.
Now organize discussion and create content specifically around their concerns. Send them an email letting them know that their ideas led to this discussion. Move people over to your side. Put those that reply into a separate mailing list and send out activities that are focused entirely upon their needs.
Then repeat with the next group.