Gap popularity is because that's what people like. Chilling and doing sim city for 45 minutes of game time, aka 1.5 hours at an average -3 sim speed. Not everyone wants to play much more challenging and stressful games. They could easily migrate to the common teamgame maps like canis, wonder, hilly, etc. if they wanted a non turtle team map, but it's not what they want. This is also shown by the lack of popularity for FAF itself: it's simply too hard and complicated to be preferable for many people. They would rather play fortnite or league of legends or SC2, etc. instead. FAF has major issues for people like the lag and pathfinding (it's almost 15 years old...), but the issue of network externalities is also massive (the more people that play the game, the more games of your preference you can find and the more you enjoy the game. E.g. I doubt you'd care so much about how many gap games there are as long as there are plenty of games that you want to play available!). But the network externalities issue isn't really solvable...it would require massive, rapid growth in the popularity of the game so that the growth can snowball, which just doesn't seem at all realistic given the market demand. The game is almost 1.5 decades old, and has fairly inferior graphics (albeit not horrible) to anything made in the last decade, and as we all know, a poor game engine leading to the performance issues.
Edit: So is there a solution? Unfortunately, none that I would put any money on. In this case I'm pretty sure pessimism is realism. Maybe you can convince all your friends to start playing, but if they are anything like mine they will try it and then quit for the aforementioned reasons. It's just not going to be many people's favorite game, and if they like it, it won't be too surprising for them to prefer dual gap anyway.