I would say that the biggest thing that keeps me playing the game is the happy joyful replies that I receive after helping out another player. Rather cheesy, but rather simple. When a player asks a question for something they are unsure about, I'm always willing to step up to the plate to give them guidance towards the answer they need. Or rather, when they request for help, I make sure to be that level 50 mercenary on standby to provide aid where it is needed. Many have heard several times, others may have heard this for the first, but as my guild mates have witnessed, as well as other individual players around that I get in contact with, each know if they need me for anything - my door is always open to them. The mass of orange text that I receive in questions, and requests for help may also play apart in the reason I remain in the game - in being glad there is still a demand for me.
I have had the pleasure of running Armed Guards "Member-Achievement" page, where I go and find (and complete myself to make sure they are fair) some of the thrilling handmade challenges for our guild members to be competitive about (I figured this would give level 50's who are bored something to do as well even though I have tiers built in for every level). Some of these challenges are things like "Timed Loot Runs" where I take note of how quickly someone can sail around and fill their cargo and port, "Solo Boss Battle: Foulberto" where pirates get strategic on how they want to fight him, and the most recent that I had came across - accidentally: "Solo Rage Ghost - With a sword".
Although most players that have been around for long periods of time might say that there are plenty of "not so kind" pirates lurking about - as a motivated player, I would also say that I actively want to be able to fulfill the personal mission of combating against that, to form a community/safe-haven that welcomes old/new and simply go out to enjoy the game and the nostalgia that it brings most of us veteran players - even if it only consists of a tight group of a few people.
It's certainly a long list - but each of these things do actively play a role as to why I am still in the game - and the reasoning as to why I will continue to be here for as long as I am able to be.