I find that the answer to why someone would stop something overlaps with the answer to another question: What is missing that, if present, would make it more enjoyable? One thing that is missing is the achievements board on the personal profile. It is even worse that it shows but also doesn't function, as I can imagine a lot of them would have lit up by now just from my recent two months back after a 9 year hiatus. I can imagine that if my crusty and bloodyminded self could like it then a kid or any adult with an even sweeter temperament and even more sensation-craving child or any adult novice would drool over it a lot more with that function working. The fact that seeing it not working pains me as much as it does tells me that a lot of people who have left, might have stayed, if only that worked. Focus more on QoL changes as well and you will see expansion. Remember, in FAF world, expansion is essential. Even if we can't expand numerically and "control more of the map" as far as people joining go, we can keep more and make the turtle stronger by enhancing the quality it has for those who, after even 9 years, never really left. That's an aesthetic thing, but think about all the aesthetics that go into the game, and which were there in some ways at the TA stage, and have only gotten better. Aesthetics is desirable not only in the game content, but also in the experience of interfacing with the gaming platform. You have to put more life into it to give it more life in this way. So fix that eyesore and I bet you'll see improvements in retention and joinership.
P.S. If you guys ever actually DO fix it (fingers crossed, the world is in hunger games mode, but just dangle the right carrot in front of the right NEET and even he'll probably do it for some choice compliments and a digital or electronic item), PLEASE make it as retroactive possible! Have it run a tally of all games already on record and use all their data to update profiles so everyone can enjoy the benefit. It takes time, and people can wait (they're already waiting whether they know it or not), but it happens sooner the sooner it gets done. Imagine over time growing a plant. You water it a little every day. Demonstrate your... affinity with the game, with gamesmanship, and with the spirit of bloodsport itself by bestowing trophies for excellence and determination, and you will see more people desiring to achieve it within the game, and more people who already do doing it more.
I look at it this way. Your intuition to include it in the first place was either well to the purpose or not. If not, why was it done in the first place? If it was, then the motive to do it to completion is manifest in proportion to the difficulty of the work. Maybe....
Have a fundraiser for it...
"Do you want this fixed? Donate the needed funds for me to take time away from other things and get it done."
And if the people here want it, they get it that way. That's crowdsourcing. So croudsource it.