"So many faces in and out of my life,
Some will last,
Some will just be now and then."
Billy Joel, Say Goodbye to Hollywood.
As in life, so it is in Forumlandia. Life has a habit of getting in the way, priorities change, people move on, others take their place. If/when newbies decide to stay, great! It gives those who are deeper-rooted in the forum a chance to get to know them and their fish/pets. Some will just need that one specific question answered, and then go about the rest of their lives. Friendships are formed, then the individuals move on, the remaining friends feel like the forum has changed/isn't the same without their friends, and that there's nothing here for them anymore, and leave themselves. All of that is fine. It's the beating heart of all forums.
The time to worry is when overall visits drop, established members who know their hobby inside out and backside forwards move on, leaving those who are maybe intermediate-level to try the best they can, but struggle. Discussions break down, the number of new threads falls. The number of newbies signing up drops drastically, and the forum becomes a ghost.
That hasn't happened here. Maybe it will in the future, but at the moment, it's still OK. Relax. Let people do what they need to do.