I think nearly anyone who has been a Game Master will agree with me; at first it's a very enjoyable experience, you do get a lot of "fame" and "glory" - but you'll also meet people who will give you a hard time for no reason at all. Eventually the cons start to outweigh the pros, and that's when most people stop caring because they aren't getting the ego/powertrip anymore.
The fact of the matter is, being a GM, particularly one with a lot of responsibility for the community as well as server side issues, isn't easy. I can see why people don't understand why we do it, and I don't think there is a simple answer to "why" either.
Everyone has their own reasons, some are negative - power, abuse via unlegit items/zeny, popularity - and some are positive - a genuine desire to help the server, to make it grow, etc. You'll find a lot of people start out with that sincere wish to help a private server prosper, but after the original hype of the job dies down and they realize how much work it is, no one wants to do it anymore or they end up going sour and corrupt.
Unfortunately there are a lot more bad Game Masters in the world of Private Servers, ones that'll give the rest of us bad names, but it can't be helped. I've never done something unlegit in my entire RO career, but I have been accused of it and people have started rumors for whatever reasons. Eventually it happens to almost anyone, no matter how nice you are or how well you do your job. So, why?
I've worked on several servers with a population of anywhere between 500 players to 1000+, I've got a lot of experience under my belt, so I've found my reason for GMing. You may call it selfish but I do it mostly for myself, and I think it's better that way. Yes, I do want to help the server, but I moreover enjoy certain aspects of the job and so I continue to work on the staff for my reasons.
I've been doing this long enough that there's no chance that I'd take a GMing job for popularity (partly because I know it doesn't work that way), nor will I be in it for the "power" (since I simply don't care much for it), and my general awareness of how RO communities work will forever prevent me from being biased. In terms of my knowledge and opinions, after a very long time, I've settled into a nice little corner and found a comfortable spot in the world of RO, and I plan to stay here.
Enjoy your wall of text! Although there's one more thing I've got to add to this;
GMing is a thankless job, often the only thanks you get is in the silence when no one is complaining.
I really think Tieria has the general idea of why it happens, and how it usually ends up, down - otherwise, a basic idea of what being a GM is like.
I've also been part of several GM teams and helper teams, and I've been from servers that have only lasted a few months, and carried an average population of 50, to servers who are still here today (even if they're barely standing), which ranged from 300-900 players. So, I can also safely say I've got a decent amount of experience in what I should and shouldn't do as a GM, as well as how to handle certain types of players. Granted, I don't know everything, I really don't think anybody does, but I do know enough to know that I enjoy being a part of a staff, or even the head of a staff, mainly because of the fact that I know I'm able to make a difference, even if it's just a notch out of a block of wood, and I honestly do enjoy being able to communicate with players, help them, guide them, and attempt to make a good community out of the server I am working for/founded.
Unfortunately, however, a lot of people now-a-days (not the whole of the staffer population, but a vast majority of them) only, as stated in numerous other topics, wish to be a part of that staff because it makes them feel important, and it they just love having all of the attention. They think that the job of a GM, no matter what the position, is a walk through the park, period. They believe that, with recognition and power, they are now better than the people they're there to support/administer. And, as, again, already stated, the minute something, even the slightest thing, goes wrong for them, they just don't care anymore. Sometimes all it takes, even, is for them to be persecuted for
doing their job. It really is kind of sad, and sometimes it's even the people who seem to have the most potential for the job. You have no idea how many people I've seen, who were actually whole-hearted staffers, quit their job over the stress that certain people in certain community force on them.
Another thing that I enjoy about the job, which I've already vaguely mentioned, is the community in general. Some people have said that there's a bad apple in every bunch, or that there's always going to be that person who tries to take you down - this is true, however, it doesn't
always happen, and I can vouche for this. Granted, there have been plenty of times where I've been given grief for doing my job, but there also have been, if not more, just as many times where I was either:
A.) Thanked for doing my job, or
B.) Everyone went on with their lives.
It's definitely not going to happen the minute your job is done, and it definitely isn't a guaranteed fact that it will ever happen to a person. I've met plenty of staffers who have managed to do their job, and never once get persecuted. Honestly, I firmly believe whether or not you're given grief off of what you do depends solely on how it was either handled, or how that person views you. You could be the nicest staffer, and someone could view you as the meanest, and that view is more than likely solely based off of something you might have said, that they might have taken the wrong way, for example. There are plenty of things that affect the outcome of such a situation, not just the fact that you're doing your job.
Anyways, like I said, I view the job of being a GM as, actually, very rewarding, even though what Tieria said is true, being a GM is often a thankless job, though not all of the time. I personally view it as, you don't need to be thanked to get a rewarding feeling from what you've done. I believe the reward comes from being able to get to know the players on a personal level (me, personally, as a staffer and a player, seeing as I firmly believe in playing on the server you GM for, even though most people believe it's impossible to do that without being corrupt), and being able to help the players out, or give them a fun and exciting RO experience.
My views may sound kind of cheesy to some people, but they're my views, and it's been that way for, basically, as long as I've been a staffer, and I stand by them strongly.