This one is gonna be a long one but bear with me. To understand what's going on right now, I think we should look at the past, what made it fun as a player, and etc.
Overall, I think players aren't sticking to the server because they don't feel obligated to do so, either through lack of fun activities or constantly changing responsibilities.
Looking back at around 2.0, I feel that 2.0 brought the most balanced and fair gameplay. Did it have meta? Yes, but that doesn't mean certain things weren't viable. Every class had defined limitations, which were capitalized on by other classes. With no levels, the power gap wasn't as clearly defined as it is currently. However, since the leveling system has been here for a while, you have players who are trying to join the server and get an idea of what the server is like, fighting people who are level 250. Think about it this way: When 3.0 was released, everyone was still on relative fairgrounds, as everyone started from scratch, and progressed together. As time progressed, power became more defined, as people like me who legit had 160 hours on the server in two weeks carved through the sith on a rampage. I will admit, that definitely ruined the server for some and I apologize. But the fact is, nobody could stop me simply because my level and playtime was just higher than others. Now, especially since the level cap is constantly increasing, the difference is becoming more polarizing. I talked about this in my suggestion post, but it just isn't fun for players to stick around to get two shot by higher levels.
And you might ask, how do we fix that? I think we, as a community, because of this indiscriminate leveling system, have become more aggressive, and want to kill most things we see for the XP. We might not be able to fix the system, but we can change the way we think and interact with others to create more meaningful encounters with new players. Sometimes you don't have to kill EVERYONE on an enemy faction, you can be chill and still roleplay in a serious manner. Players shouldn't be waiting outside the community center so often to jump another player walking out. There are times where perhaps we may be killing people because we've deemed them personal enemies, but I'll get to that later. Point is, roleplay between factions doesn't always mean a bloodbath, it can mean interactions of dialogue, story, espionage, etc. It is a positive note that we are attempting to move towards an attitude of serious roleplay, and that should be praised.
On the note of roleplay, I feel there isn't enough weight behind every player's story now. I feel like every day that a player gets on, something meaningful should be happening to them personally, like training with their master and defeating a few sith together, bringing the padawan and their master closer together. Just small awesome moments like that, which create positive memories of the server to individuals. I remember training with Artorias one day in 2.0, and he helped me train to understand how to duel, and I thought "man, this is pretty cool, I'm gonna win tomorrow when I get on again". That spark eventually begins to fade over time, as the moments will start to lose their individuality, thus lessening the positive experience of the user. There are limits to everything, but we should be actively trying to create positive experiences with others and make the magic happen. Currently, I think (and this isn't fact, this is just what I THINK is happening) new players are getting destroyed by old players who have significantly more power, which doesn't really create positive experiences. On another JvS server which I played, I walked up to opposing faction players, and I said I was new and asked how to play. They showed me around and told me how most of the stuff works rather than killing me; I want to see more experiences like this happen to new players, they should feel connected.
Now onto the note of responsibilities: Think about the role of leaders, whether it be council or emperor, etc. It is bound to get stale after a while, and sometimes people can't find suitable replacements for themselves, causing deteriorating standards of quality (not bashing on any current leaders, just saying this happens sometimes/eventually). The positions just become the same eventually, Council is just council, and eventually, you run out of things to do to become even stronger. When I was wrath, I got sick of people just wanting to duel day in and day out, what was the point of being the position if it's not fun? So I just gave up, left it all behind, and that was that. People will eventually get tired of being a high power in the server, and they'll leave. You can't really stop it, and the old players who played have had their fun and gone. We just have to encourage and help the new players grow to take our places one day, becoming a positive force for other new players who join after. As I've already talked about the attitude towards new players, it's an innate flaw of the leveling system.
There's also the lack of purpose and content which we are lacking in compared to some other servers. Other servers have capture point systems which reward players with XP and etc. The majority of the enjoyable new content comes from events, which also eventually become repetitive after a point. It all gets lacking eventually, and the rushed lacking release of 4.0 doesn't help this. Players want content which can keep them in, giving them a sense of purpose, not gambling or busted executions. Distributing more and more items to players doesn't help either, it just makes the economy wack and provides only temporary satisfaction rather than solving the issue of gameplay other than "Kill other players on the server because why not", which I've already talked about and we should generally be striving to avoid.
I know this post has been long, but I think the main issue just revolves around the community's perception and attitude of what we should be doing, and we should be trying to change this, even if it's hard.