Ok. Thank you everyone. I have learned that the norifications are only working for the original poster. (thread creator).
There should be a way for others who replied to the post to subscribe to it and receive notifications on new replies to the thread.
This is why topics are dying on the forums and in the groups. Another way to achieve this would be by adding inline comments to individual posts (replies) like the SpaceHey Buletins have. Then people would receive notifications on new replies to their posts and the discussions would continue growing.