There is a problem with PC Graal where every so often all the players on my server are disconnected. I believe this drives playercount down for PC Graal in general over time because less idling players means lower playercount resulting in less logins from new or returning players. It's a negative feedback loop which results in the playercount systematically lowering itself. If this bug were fixed the negative feedback loop would become a positive feedback loop where idling/playing players grow the perception that a server is worth playing and therefore more players return and more new players log in.
Edit: ironically as I was typing this it happened to me again