Hey there, and welcome to our forums! Glad you found us here. There are several opinions and explanations depending on who you ask, and here are my thoughts. As you said, we have a good number of people on our Discord and forums, and a healthy amount of discussion on top of that! I'm actually very happy to see our community as reached this point.
To see the same activity in our game servers is a hit or miss, and that can be common for other communities too. What I think happens is that players would open up the launcher and find that 0/40 or 0/127 staring them in their face and get turned away. Understandably, no one wants to join an empty server. However, a server does not populate until one person joins. Then the next user notices the playercount change, and they join. Then the third, then the fourth, and so on. The snowball effect does wonders for our games, and combined with our Discord, games fill up easier than ever! (Disclaimer: this may have limited effect on the multiple Renegade servers I see in your image, such as Area 51 AOW, Rencorner Snipe, etc. Though we support them, our Discord is linked to our in-house projects: APB, IA, TSR, ECW)
Which mods/servers are you looking for players in?